Heat Pump Water Heaters | Hacker News Reader

Heat Pump Water Heaters

energy.gov

157 pointsbranko_d214 comments

I've had mine for about a year. I put it in my garage which previously, would reach easily 100F + in the summer. This past summer, on the hottest day, it got to about 90 in the garage. When the water heater was running, it easily kept the garage below 90. I purchased the hybrid version which can use straight electricity when the heat pump won't cut it. This serves to also keep the garage cooler for the second fridge I have in the garage.

I was previously on propane to heat my water, which was costing between $50 - $60 a month. During the summer, my electricity bill only went up $12 a month. During the coldest part of winter, it was at about $30 a month more. But, I pay considerably less for electricity in the winter than in the summer.

Just for reference, I purchased the Rheem 65 gal 10 year warranty from Home Depot when it was on sale. This has definitely been one of the best purchases

50$ a month for hot water seems really high? I’ve never gone over 20$. Anything you want to tell us?

Water usage basically scales with household size. GP probably isn't a single dude living in a studio apartment taking navy showers and planning his meal prep to minimize dish washing. Combine that with an electric water heater (almost always more expensive to run than natural gas) and a nearly triple digit electricity bill isn't surprising.

Propane, I’d guess. With propane, you are paying someone to truck propane to you and pump it into your tank. You are also paying all the costs of owning and maintaining the tank.

If you live in a place with reliable electricity, I don’t think propane really makes sense any more. You can get heat and hot water from heat pumps, and induction stoves work well and are vastly more efficient than gas.

In rural areas, where propane is common, with some density (1-5 acre lots), lots of places converted to natural gas after the fracking boom.

That’s not to say that propane is still not common.

You get natural gas delivered? What’s so special about propane anyway that it’s the defacto portable gas?

It’s liquid at ambient temperatures under pressure so it transports and stores well. Also it’s a tad more energy dense than natural gas.

Propane has higher energy density, can be liquified by compression, and doesn't need cryogenic tanks.

Propane is easily transported and stored as a moderately pressurized liquid at ambient temperatures. Propane has a big volumetric advantage over natural gas. Natural gas is mainly methane, liquifies at -160°C, and requires active refrigeration. If your use point is within natural gas piping range, gas is usually the better choice. Propane is the choice for locations not served by piped natural gas.

Fun factoid: Propane leaks are far more dangerous than methane leaks. Methane is less dense than air, so it tends to mix more fully. But propane is more dense than air, so it tends to pool near the floor. And the lower flammability limit for propane is lower (2.1% vs 5.0%). So you reach the lower flammability limit faster. Plus the fact that pilot lights are often near the floor.

Induction is alright, and some people prefer it. Vastly superior to radiant electric.

If you really like cooking on gas (I happen to) the expense of running a propane range is insignificant compared to the amount of propane you'd burn to heat water or a home.

Why would you go with propane? Natural gas is ubiquitous and everywhere (at least in the US). Maybe it's less so in the south? In the north it's mandatory for not dying in the winter unless you're so rural that you need to chop wood to stay warm.

in rural Sierra Nevada foothills California counties there is not ubiquitous natural gas

No, natural gas is not ubiquitous. Maybe within certain urban and suburban areas, but once you get a little rural you are out of luck.

Then again, a lot of people don’t realize cable internet isn’t a given, even within 15 minutes of the capital city of a state in the contiguous United States. They also don’t have natural gas available. :-)

Water and sewer too.

Copper telephone and electricity are the only two utilities you can count on in the most rural 10% of America.

In rural eastern Oregon, there is not ubiquitous natural gas.

I don’t think anybody chooses propane over natural gas, but natural gas is unavailable to a great many people.

In suburban NY you don't have ubiquitous natural gas. Some, but not all, new developments are natural gas, but many existing ones are heating oil. Propane is also a possibility, but much more expensive so is not used as often as oil except for cooking.

Before we a) put in PV and b) got that heat pump water heater, we paid about $50 for our hot water heater electricity use (~160kWh/month) here in HI.

Wow, I'd never considered that aspect of a heat pump before. But it makes sense -- a heat pump is (conceptually) just a backwards air conditioner, after all; it stands to reason that it'd make the room colder while it's operating.

My thermodynamics book in college (Cengal and Boles?) had a (Blondie) comic with The exchange:

“Are you air-conditioning the outside?”

‘No, I’m heating the house!’

I replaced our older electric water heater with the 50 gallon version of this last month: https://www.homedepot.com/p/Rheem-Performance-Platinum-50-Ga.... The heater was about $1200, the rebate from the state of Vermont was about $800. I did the install myself with about $100 of parts.

Positives: As far as I can tell so far, the savings in electric usage should pay back within 2-3 years. It has a 10 year warranty, which should keep it working for a while. If the compressor fails, there is an electric element as backup. The device itself seems solid and well built.

Negatives: Even though it's in the basement, it's louder than I'd like --- about like an window air conditioner. Getting it down the narrow basement stairs (and getting the old heater out) was hard. Reheat is fairly slow if you keep it on the highest efficiency "heat pump only" setting. I've yet to get the phone app working to control it from upstairs. The basement is quite cool (especially in winter) so I'm worried it won't be maximally efficient. It produces a small amount of condensate water, which requires a drain of some sort.

Overall, I'm hoping it will be a win. It produces enough hot water for our 2-person needs, and seems like it should be more efficient than what it replaced. If you are considering one, it's worth thinking about the cooling effect that it will have on the room that it is in. If you already run an air conditioner, this is a win. If you are heating, this is a loss. We heat with wood in the winter (which is inexpensive if you cut your own) and don't have any other summer air conditioner, so for us this aspect is fairly neutral.

This model can be ducted with standard 8" ducting. It is possible to have it draw warm air from outside or vent the cold air out of the house. You can get fancy and install baffles that you switch seasonally. A properly ducted system will be more efficient because you won't be putting artificial house heat into the water or heating the house more to offset the cooling.

I installed it thinking I'd install ducting if necessary. But as you might guess, in the winter in Vermont there aren't a lot of available sources of warm air other than the those you create through heating. And if I vent to the outside, the resulting depressurization will just cause the rest of the house to suck in even colder outside air. The basement itself derives enough ground heat to stay above freezing, but heat pump efficiency drops as you get close to freezing.

Currently, I think I'll probably connect to an intake floor register from above, so it has better access to warmer air. I'll be trading off more firewood for less electric, which is probably a win. I'll probably also exhaust the cooler air back into the house level, on the theory that this will help a little in the summer. I'm guessing the downside will be increased noise. It's a quiet house to begin with (woodstove with no forced air) and I'm loath to make it noisier.

Do you know if there is any benefit to going with the model specific ducting kit? Or can one just buy off the shelf?

Off the shelf should be fine. It's rated for 340' of ridgid pipe or 125' of flex. I've seen people zig-zag the ducts to help reduce the noise

> We heat with wood in the winter

You should stop doing this. The impact on air quality is very bad and is disproportionately bad for the people nearest the source (i.e. you).

https://www.lung.org/clean-air/at-home/indoor-air-pollutants...

https://www.epa.gov/burnwise/wood-smoke-and-your-health

I'm not disagreeing that wood burners have a negative effect on air quality, but there are plenty of valid reasons to burn wood for heating. Not having access to a stable uninterrupted electricity supply is one reason. Cost is another reason. A good cast iron wood stove can be quite efficient and will continue to put out heat long after the wood has finished burning.

Yes, we should all aim to pollute less. But we should not attach stigma to things that for many people is their only choice of heating, transport, etc.

> Not having access to a stable uninterrupted electricity supply is one reason.

Non-electric heating systems use relatively little electricity, to the point that a small inexpensive solar panel and battery would suffice. Some don't require any. Also, this criteria doesn't apply to the vast majority of locations which do have access to the power grid.

> Cost is another reason.

Cost is generally regarded as an invalid reason for pollution. Surely it costs less to dump industrial waste in the river as well.

Also, how much money is your health worth to you?

> A good cast iron wood stove can be quite efficient and will continue to put out heat long after the wood has finished burning.

This kind of system is less efficient than modern heating systems designed for fuel efficiency, which run only when they're needed and only to the extent they're needed. Storing heat in metal rather than burning fuel as needed means burning more fuel at the start and less later, which means a greater temperature variation and more fuel required to maintain the same minimum temperature, which exacerbates the level of pollution being generated.

> But we should not attach stigma to things that for many people is their only choice of heating, transport, etc.

We should attach a stigma to things that have negative externalities, because they have negative externalities. If some people can't afford it then give them money instead of overlooking the harm they cause.

>>Cost is generally regarded as an invalid reason for pollution. Surely it costs less to dump industrial waste in the river as well.

You know, I'm feeling idealistic like this quite often, but then the reality hits hard sometimes. In Poland where I'm from apparently 35% of residential properties still use coal for heating in 2020, which to my modern sensibilities is insane, but then I speak to some of my family living outside of the cities and the reality is:

1) there is no mainline gas supply, so gas is not really an option, unless you want to pay a lot of money to have an external tank installed at your property(look at point 3)

2) electricity is far too expensive to use for heating, every back of a napkin calculation shows that it would simply eat your entire salary to heat using electricity in colder months. Electricity in Poland is both hugely expensive and almost entirely from fossil fuels, we produce most of our electricity from coal power plants(and building more of them!). I can keep telling people that "surely their health is more important than money" but it would literally by a question of "heat or food for the month" if they used electric heaters.

3) there are some "eco" options like converting your boiler to eco-pellets, but even with EU grants, realistically, it's still like 2-3 months worth of salary to fit a new boiler for a lot of people. Simply not an option.

4) coal is very very cheap. You can buy supply that will last you entire winter for about ~400USD, maybe less if you're willing to burn poorer quality coal(which theoretically shouldn't be burnt anymore but yeah good luck enforcing it).

>>If some people can't afford it then give them money instead

Again, that's cool as an idea, that's just not how it works in reality.

If you think the presence of a power grid is the same as having power 24/7, you need to spend some time in other parts of the world. In some places you are lucky to have power for 12 hours a day.

You're looking at this from a position of privilege. When I say "cost is another reason", what I'm really saying is that many people literally can't afford the electricity or the electric heater itself. The vast majority of the world's population earn no more than a few US dollars a day. They are saving for their next meal and hoping they can afford to have their shoes repaired soon. They aren't in a position to consider how they can be more environmentally friendly. They just want to survive.

You can buy catalytic converters for wood stoves.

Also, as long as you have some draft, you can add wood without releasing much indoor smoke.

> You can buy catalytic converters for wood stoves.

This is kind of like saying you can buy a catalytic converter for your car in 1950. It costs money and much of the benefit goes to people who aren't you so most people don't buy them unless required by law. Also, they're not 100% efficient so although they are an improvement they don't fully eliminate the problem.

> Also, as long as you have some draft, you can add wood without releasing much indoor smoke.

Indoor smoke is really bad, like catastrophically bad, but outdoor smoke is no fun either. It accumulates in the area and ends up back inside. This can be really bad whenever it isn't windy.

> Also, they're not 100% efficient so although they are an improvement they don't fully eliminate the problem.

True, but they're up near 90%, I think. And they also increase heat recovery efficiency, so you'll need less wood.

Consider chilling out on this a bit... There's a huge difference between a fireplace and a modern high-efficiency wood stove or pellet stove. The latter produces mostly CO2 and H2O, with far less particulate. Look at the chimney of one while running at operating temperature and it will be clear (no smoke).

Furthermore, not everyone can afford other options. It's just the way it is. I'd love to cover my roof in photovoltaic panels and get an electric car, but I'm too poor. Maybe in 15 years, if I keep savings like I have.

If you live in Vermont and burn wood year round you're probably still better off air quality wise than living in a city.

I also live in Vermont and my rates are high but decent at .115 a KwH for the first 200. After that they jump to .255 a KwH. If I did everything with electricity it would cost me $50/Mo for heating water and about 300/Mo for space heating. This is pretty close to what propane cost me back before oil prices crashed.

This is using ideal numbers from manufacturer sites and energy.gov. Given that it's Vermont and it can stay below freezing for months at a time (my basement stays around 45 in the Winter) I'm not sure ideal numbers are...ideal.

This stuff gets complicated and includes social factors, inertia, installed base and regional issues that almost certainly don't apply to you.

I recently installed a wood pellet stove which is both cleaner burning and more efficient than a wood stove. It's great. It saved me more than 50% off my heating costs. However,it's noisy, has failed twice in two years requiring expensive parts and repairs and still doesn't work when the electricity goes out. In rural Vermont you can expect at least one power outage per year that lasts more than 24 hours. Last year we had one that lasted 60 hours. Fortunately it was Winter so it was 6 degrees in the basement where the freezers were and we didn't lose the food.

Unfortunately it was Winter and our pellet stove, propane boiler and space heaters all require electricity to run so we spent a few very chilly days in a 6 degree house.

Let me start by saying I really appreciate your comments on this site. I upvote a lot of your comments on a lot of threads, and appreciate seeing what you have to say. But although wood heat is a complex issue, I don't think you are correct here. Having looked at it pretty closely, I think modern wood heat is good solution for homes in the rural Northeastern US.

Yes, air pollution is a big problem. Modern catalytic stoves are much lower on particulate emissions than older models. The one we have (https://www.woodstove.com/index.php/progress-hybrid) has about 1/10 the emissions of older models. Efficiency is also about 30% higher, which reduces CO2 emissions. With a reasonably designed system (draft that draws in outside air) indoor pollution isn't particularly an issue. Locally harvested wood is quite sustainable, and very close to CO2 neutral. We manage our forest land, and cutting wood is an essential part of this management. And mentally, it really is pleasing to feel in control of the whole process --- cut trees, burn trees, grow more trees.

Since we're not on natural gas, the best alternative at this point would probably be a solar system and an electric heat pump. As we get older, and are are less able to harvest our own wood, we'll look into it more seriously. I think for right now, though, wood burning makes good sense for us both financially and ecologically. That said, I would be interested to see any sources you might have that compare modern efficient wood stoves with the alternatives.

> It has a 10 year warranty

...

> I've yet to get the phone app working to control it from upstairs.

I wonder what the phone app support will look like in 10 years...

I wouldn't try and cool down a garage or try and maintain a temperature in it to be honest, they're usually very poorly insulated so it'd be a huge waste of energy.

Wouldn't it be great if your fridge could integrate directly with the heat pump, rather than indirectly via the air in an enclosed space?

In summmer, our (California) home frequently has the air-conditioning running mid afternoon, at the same time as a gas boiler is heating the pool. It would seem to make sense to use the pool as a giant heatsink for the home AC... but that doesn't exist apparently, and any plumber I talk to looks at me like I'm crazy. "They are separate systems."

From my reading of heat pumps, mismatches in energy sources and sinks can make linking things together more complicated (aka more expensive) than is commonly available.

For the pool <-> A/C case, This Old House did a segment on linking the systems: https://www.youtube.com/watch?v=J7fB8ul9dZw

Edit: chris_va has more details about why linking systems is hard: https://news.ycombinator.com/item?id=23001888

Would be great if everything was integrated. Computers for example generate a lot of heat. Would be great if we could easily move that heat to places where it is actually useful instead of just wasting it. Looks like this is a thing in data centers:

https://en.wikipedia.org/wiki/Temperature_chaining

> It would seem to make sense to use the pool as a giant heatsink for the home AC... but that doesn't exist apparently, and any plumber I talk to looks at me like I'm crazy.

You are not crazy. IBM did that.

https://en.wikipedia.org/wiki/Green_data_center#Reusing_wast...

> The IBM Reusing Data Center in Switzerland, where the heat warms a local swimming pool

Also:

https://en.wikipedia.org/wiki/Data_furnace

It does exist, and those plumbers are wrong. The biggest challenge is finding a heat exchanger (to replace the one in your AC condenser) which is designed to survive highly corrosive hot swimming pool water.

The UCDavis Western Cooling Efficiency Center [1] has done extensive research on this, sponsored by the California Energy Commission.

In a nutshell, they found that using your swimming pool as a heat sink for your air conditioner can reduce cooling energy consumption by 30% or more (not including the reduction in pool heating energy consumption). The two main caveats:

1. Many pools are too small relative to the house to be an effective heat sink without overheating the pool.

2. Increased pool temperature causes increased evaporation, resulting in increased water consumption (also a problem in CA).

They also found that adding a fountain for evaporative cooling of the pool can mitigate #1, at the expense of worsening #2.

[1]https://wcec.ucdavis.edu/

I like the idea but I can't find a brand that I'd trust in this day and age. Whiteware goods used to last 20yrs, or people expected them to. Nowadays 5yrs warranty seems to be the timeline they're expecting people to accept.

Heatpump water heater will save energy, but more parts to break. I'm sure it can be engineered to be reliable, just not sure by whom...

I have heard AO Smiths are good units. I personally have never used one though.

I know this is not a concept people are used to, but I’m really in to the idea of open source appliances. In that case there’d be one centralized (and forkable) project where skilled engineers from around the world could design a suitable machine. I’d love to see companies pop up to manufacture those designs the same way 3D printer companies have done.

That’s a great idea. If you had enough money you could hire engineers to make version 1 and kick it off. Or maybe you could recruit some engineers?

Well I try to encourage bored engineers to work on open source hardware projects. Finding a funding stream is difficult but finding engineers who want to improve their skills and contribute to society is pretty doable. I spend half of my working time on unpaid open source work that is self directed and primarily chosen based on what is fun and enriching. I have a YouTube channel where I am slowly trying to get the message out, though it’s hard to put all my theory in to words and shoot videos for it. I seem to prefer doing engineering over writing scripts, though writing scripts has its place.

That’s great! What kind of hardware projects?

Well recently I designed a nice 3D printable pair of headphones that I will be publishing in the next month or two. For $50 they sound as good as the $200 headphones my roommates have (halfway decent drivers make the difference).

My big open source work has to do with 3D printed robotics and computer vision. I designed this robot which is CC0 open source. I am using it for computer vision research:

https://reboot.love/t/new-cameras-on-rover/

https://imgur.com/gallery/GqXD2Zj

Wow I love that robot! I’ve actually been wanting to get into robotics and computer vision myself. Drop me an email if you want to chat robots sometime.

How does liability work for open source appliances? That’s the first thing that comes to mind when doing business in the US, especially with a product that can cause carbon monoxide poisoning or fires.

You'll probably have a tough time even installing it legally under many building codes.

I don’t see why an open source design manufactured by a competent manufacturer would be any different from a proprietary design. It would need to pass certifications and the regulator may require a version freeze, but it seems like it could be done.

There’s also countries all over the world who don’t have these regulations, and would appreciate good quality plans for useful appliances.

IANAL. I imagine a manufacturer would assume liability for an appliance based on an open source design, assuming the design uses a typical open source license that disclaims liability. I'm not aware of a reason why an open source design for a physical product would be different from open source code in this respect. If the manufacturer paid to get the designs reviewed by an engineering firm, maybe they could pass the liability off to the firm for a design defect, depending on their contract?

A lawyer told me once that open source code used in a nuclear project could maintain liability for the original author, but I can't find any evidence to support that. The Paris Convention seems to place strict liability on the nuclear operator with no mention of such an exception.

Open source firmware works great for several devices that I use daily.

My router- I'm using an Asus NT-16[1] with EasyTomato for several years, and it's working flawlessly. I know others are using Pfsense also, which seems to work great for geeks.

I have an old iPod 5.5 gen running rockbox, an open source firmware.

I also use OpenVix[2] firmware, flashed onto a set-top box capable of DVB-T2, DVB-S and more (this model[3]) which also works great. The interface is similar to Sky commercial STBs, and there are ways to reorder and group TV stations with external editors. Therefore, its UI is on a par with commercial providers, and it's extensibility and flexibility is way ahead.

My experience with open source firmware is great, it's stable, secure, you potentially avoid unnecessary e-waste, and you're not locked into a manufacturer that might discontinue support for the device, so it would be very exciting to see this extended to white-goods appliances also.

[1] https://www.asus.com/Networking/RTN16/

[2] https://www.openvix.co.uk/

[3] http://vuplus.com/sub/sub0113.php

They do have more parts, but these units are basically a heat pump mounted on top of a water heater. It's more complex but not absurdly so.

There are only four manufacturers who sell hybrid heat pump / electric water heaters in the US. Other brands are rebadged.

Namely:

Rheem, AO Smith, Bradford White, and Stiebel Eltron

All four brands offer 10 year warranties.

Heat pump water heaters have very slow recovery rates compared to gas, so I would buy the largest unit you can fit. That's usually 80 gallons, but they are very tall (due to the heat pump) so it depends on the space.

UEF varies from 3.3 to 3.7, and prices range from $1700 to $2400. The lowest TCO is a Rheem unit at an estimated $3310 over 10 years (purchase price + electricity).

Rheem is currently ahead of the others on efficiency and Stiebel Eltron is probably going to be difficult to find service for in the US. The other two are middle of the pack.

Appliance manufacturers aren't hiring dumb engineers. The same engineers they already employ could design appliances to last 20 years, 50 years, or 100 years.

There were more robust consumer appliances on the market, and they were mostly pushed out of the mainstream as consumers greatly preferred to buy value engineered products at a fraction of the price. You still can buy more robust products, but they don't exist at the value-engineered prices people now expect.

Look up the prices of mid-century appliances and adjust for inflation. Let's use a simple toaster for example, because they haven't changed much in design or function:

https://www.atticpaper.com/proddetail.php?prod=1957-ge-toast...

That's $280 in today's dollars.

If you look at similarly priced toasters today, you probably get a better toaster now than you did then:

https://www.webstaurantstore.com/avatoast-thd27240-heavy-dut...

But nobody buys these for home use because the ROI will never pay off. A series of $20 toasters over a lifetime will never catch up to the initial investment of a more robust toaster. Plus, people like having new stylish appliances as trends change.

TL;DR: people say they want reliable appliances, but they actually don't.

When my water heater last needed replacing I went and got a Propane Condensing Gas Tank water heater[1]. It was a bit expensive up front, but at 96% efficiency I thought I would make up the difference on gas while enjoying the performance. It is pretty wild - we lost power for days once in the winter cold, and it brought the water back up to temperature in under 10 minutes. Even empty it can basically keep up and heat like a tankless unit would.

It has a little LCD panel where you can check the stats of the unit, so I just took a look. We've had the heater on for 3430 days, it has cycled 15,584 times, and run the burner for 57 days. It has basically run about 1.5% of the time it has been on.

In the future I'd consider going the heat pump route if I can get solar, but given the topology and how my house is positioned it doesn't look like I'm a great candidate for it :-(.

[1] https://www.hotwater.com/water-heaters/residential/high-effi...

I had not heard of Condensing Gas Tank water heaters before. They are very clever. Gas water heaters are very popular here in New Zealand. Do you know how much more efficient the Condensing Gas Tank water heater is over regular gas?

If I understand it correctly, the difference is that the condensing system pre-heats the cold water with the exhaust gas from the burner.

https://www.hotwatercylinders.nz/images/source/Bosch_26eco_C...

Did you compare costs of a regular gas heater vs. condensing?

Best case, a condensing heater uses 20% less gas than a conventional one. But there are some caveats...in order to condense the exhaust fumes, the returning water has to be cold enough. Low temperature radiators or underfloor heating are best for that. If you have huge, old, cast iron radiators that get super hot and stay hot for a long time, there probably won't be much condensing going on.

Basically any time you see white smoking coming out the flue, it's not condensing.

I believe a standard gas water heater is about 78% efficient, for a net gain of 18%.

It does generate condensate, but since my gas furnace is near by I was able to set it up to use the same drainage system.

The unit was about $2500, versus probably something like $1000 for a more "standard" power vent unit. So $1500 to make up, worst case.

It burns 100,000 BTU an hour when it runs. A gallon of propane is about 91,500 BTU. So every hour is around 1.1 gallons of propane. The unit has run for 1368 hours so far, resulting in it consuming around 1505 gallons of propane. Assuming I would have used 18% more propane for a regular heater, that would mean 271 gallons saved. Propane cost fluctuates a lot here, but if we just run with a $2.50/gallon average, then it has saved me something like $678.

There are a bunch of things I don't know though. For example, I don't know if this unit retains the heated water better than their lower/standard ones. I suspect it does given how infrequently it runs. It's design is also supposed to maintain its efficiency as it ages versus losses from a "standard" burner setup. True story or marketing shenanigans, I don't know.

I was able to take advantage of a government program at the time to get a tax incentive on the heater due to its efficiency. I don't remember the exact amount, but I'm likely about even on it now between the incentive and the recoup.

But, discarding that, I'd be about 50% recouped and have had a great hot water experience. It just never runs out, it rarely runs when there isn't an active draw, it only operates for minutes when it does run, it's LCD/metrics scratch my geek itch, and it's probably the best I can do for the environment given my constraints.

Is a condensing gas tank water heater what we in the UK would call a condensing boiler?

If so, in the UK, it's been legally required that all new boilers are of this type since 2005. I'm a little bit surprised they aren't better known in the US.

Why aren't there integrated systems for heating/cooling? (Or maybe this exists and I just don't know the proper terms to search for)

We have multiple cooling devices: air conditioning (dumping heat outside) and refrigerators (dumping heat inside). Then we have multiple separate heating devices: furnaces and hot water tanks that burn electricity or gas to generate heat.

I've always thought it would be more efficient if these units were all connected with some kind of coolant loop, and a heat pump / control unit that could route heat/cooling to where it's needed.

I did find a similar system for connecting air conditioning to heat a swimming pool (instead of outside condenser unit), which is pretty neat, but I'm thinking bigger. If you're going to dump excess heat anyway, might as well use it to heat water, at least.

Then, when it inevitably breaks, your house is cold, you have no hot water, and all your food is spoiled, all at the same time.

I nominate you as the new Secretary of Food Distribution.

Systems like that are floor radiant heating using pex water tubes embedded beneath the flooring. Geothermal heatpumps circulate water loops into the ground to dump heat in the summer / grab heat in the winter.

> Heat pump water heater systems typically have higher initial costs than conventional storage water heaters. However, they have lower operating costs, which can offset their higher purchase and installation prices.

That's the key problem. Solar cracked this nut with the PPA -- zero upfront costs because the system is financed, you pay your monthly electric bill through the solar company, and they take a cut of the "operational savings" as loan servicing and profit. However, the PPA was an uphill battle -- it took a while for big finance to be comfortable with the long term performance of solar panels before they became comfortable doing this kind of loans. The big solar companies today are the ones who took a bet on making PPA financing possible.

With home efficiency improvements, however, there are so many more variables. Whereas solar is basically the panel and the inverter, with home heating you need to factor in the construction of the home and a million other variables. If the efficiency paybacks are less predictable, it's harder to finance, so it's harder to overcome the higher upfront costs.

> Why aren't there integrated systems for heating/cooling? (Or maybe this exists and I just don't know the proper terms to search for)

There are some cases where such integration can be achieved through clever design (i.e. a heat pump water heater that dumps cold air on an adjacent warm kitchen), but many times the loads of the heating/cooling use cases don't match up well either in magnitude or timing.

A pool pump is an interesting example where the pool likely has enough thermal mass to absorb the heat from a house via a heat pump, although at some point the pool would likely get too hot after days of repeated heating, since it would hold on to heat longer than the adjacent house, so it would only make more sense in areas with large day/night variations in temperature, like in high deserts.

Japan do have such system though not for export as they're still iterating through at their own pace. Daikin do used to have an Altherma product for sale, but heatpump for heating isn't as nice as gas furnace if you consider the fact that body temp is usually higher than the temperature heatpump outputs at efficient levels.

For example, to heat a room to 70 degrees indoor meant if they can output heat at 75 degrees then it'd be sufficient, unfortunately no one would want to have 75 degrees wind blowing on them in winter. We want something like 150 degrees so it actually feels warm.

That's actually one of the general issues with heatpumps - because they aren't literally lighting something on fire (or using resistive heating which just lights money on fire) they have smaller temperature deltas when designed properly as you mention. This leads to things like oversized air conditioners in hot places because people will cycle the AC creating a high peak demand and if it isn't 'blowing cold' they think it isn't working.

Heat pumps (assuming they can vary their output, which most new ones can) work much better to keep a constant temperature whether hot or cold and actually create a really nice indoor environment if a) designed or sized correctly and 2) have good thermostat placement. There's plenty of software, standards, and guides out there to hit both of those and then you just have to educate the users to set a temperature and then forget about it other than monthly filter cleaning. This is hard coming from 100% or 0% duty cycle systems like most fossil-fuel heat and old-style air conditioners so some think heat pumps are 'wimpy' and don't work. Placement is also part of that - you shouldn't be sitting in the output of the unit (which tend to be lower velocity than forced hot air etc) because the unit should be placed so it can cool the entire space.

>We want something like 150 degrees so it actually feels warm.

The reason why you want the air cooler in the summer and warmer in the winter is to achieve a similar (comfortable) rate of heat loss through your skin. The reason why that feels different even at the same air temperature is due to humidity and radiative heating differences. Your HVAC isn't just heating and cooling you, it's also heating and cooling all of your walls. If your wall temperature varies by 10 degrees between summer and winter, even with the same air temperature, it'll feel different because of the increase or decrease in infrared coming off of the walls. The better insulated and less leaky your house is, the lower that differential will be. If you could run radiative cooling through external walls and ceilings, you would only need a fraction of the typical air movement in a house for ventilation and you would still feel totally comfortable.

We don't need to heat rooms with body temperature ventilation, we just need to keep a comfortable rate of heat loss for human occupants. That's dependent on radiative heat, air temperature, humidity, and air velocity.

You'd probably need a large house and a small pool in Florida for that to be the case.

Pools are typically uninsulated and also experience a decent amount of evaporative cooling. It is not uncommon for swimming pools to have heaters with double the output capacity of the furnace in the home they're attached to.

What I am guessing:

Appliance cost: You can get a $500 normal fridge with 100's of choices or the one $2000 integrated with the home system one that does the same things from a specialist supplier. Then factor in integrated appliances / size of fridge for spot.

Installation cost: In the order of $1000s for parts and labor.

Installation authority: If you are renting, or need building owner permissions (e.g. an apartment) then no chance.

The only people buying this are those "grand designs" type people who are architecting their own house with say $1m build budget and want to be "eco".

> The only people buying this are those "grand designs" type people who are architecting their own house with say $1m build budget and want to be "eco".

Sad but mostly true in the US.

High efficiency appliances are market segmented as luxury goods, therefore mostly purchased by the well off, limiting the energy used reduction impact of the technology.

This is less the case in societies with high energy costs, like Japan or parts of Europe.

Heat pumps are not a new technology - they are air conditioners that can be run in reverse, and in a broader range of conditions.

It’s a luxury good because it’s more expensive than natural gas in the US. Natural gas systems are cheap, easy to work on, and resilient because they can continue working even when the electricity isn’t (especially nice in winter during snow storms).

> because it’s more expensive than natural gas in the US

Assuming the antecedent for "it" is electricity, yes - on a per BTU basis nat gas is cheaper, but the beauty of heat pumps is that they move ambient heat instead of releasing it from chemical bonds, so they cost about the same to operate as nat gas water heaters.

Coupled with solar, their operating coat gets even cheaper.

I agree that they are more expensive to build than a simple nat gas heater, but they also don't need exhaust ventilation ducts. Also, higher efficiency condensing nat gas furnaces are also more expensive, requiring fans to force cooled exhaust gases out of the exhaust.

> easy to work on

This is the reason everyday non green-focused HVAC contractors have given me for why they don't install heat pumps. They and their crews aren't familiar with them.

Natural gas is available to a large fraction of the US population, but not a large fraction of the landmass. Something to keep in mind.

There are thermal battery suppliers out there (a quick search turned up Sunamp, one I hadn't heard of before) that can be part of that kind of system. Geothermal heat exchangers as floatrock mentioned are probably the cheapest general version that use the ground as a thermal battery but don't typically have interlinked systems - and they're much more than a typical air-cooled system.

The show This Old House showed an interesting system a few years ago at [1] that used liquid loop HVAC components and thermal batteries as a tech demonstrator. There's also systems in newer high rises that have linked loops such that the hot side of the building (sun-facing) can pre-heat the heat pumps of the cold-side (shaded) portion of the building. These rely on advanced systems that don't tend to be deployed in homes (utilizing newer building management systems and newer HVAC like variable refrigerant flow to get the best efficiency).

Ultimately, things like this are expensive and uncommon so require per-site design that very few can justify because the payoff period is pretty long as you have the one-off cost of the thermal battery and often higher maintenance costs because you need someone who understands the system.

[1]: https://www.thisoldhouse.com/ask-this-old-house/21016105/fut...

Lot's of small reasons.

You don't want to transport heat a far distance (thermal loss becomes too high), so keeping the vent for the refrigerator integrated into the unit is generally better than shipping it off outside.

CoP is the lift you get from a heat pump given a specific delta-T. The smaller the delta-T (like an air conditioning unit's 90F->70F), the more efficient you can make it. If you group a bunch of components together with different target temperatures, you'd either effectively have 2 lines (so 2 systems), or run the system at the lowest temperature you care about. 2 systems is what you have today, and 1 system with high delta-T would have a much worse CoP.

And other reasons...

Also refrigerant has a very high carbon cost and installing piping on site between all of these appliances would require more refrigerant to fill those pipes and a higher potential for leaks.

Refridgerators are pretty low power. Transporting heat works fine for tens of km in district heating. But you probably have some better energy efficiency investments than building insulated pipes and a secondary water circuit + heat exchanger or running long stretches of expensive refrigerant in the pipes, for the fridge's 50 watts worth of heat.

>>Why aren't there integrated systems for heating/cooling?

See Mitsubishi's Mr Slim line. They need to do a better job promoting it, but it is amazing.

Why not do it like the commies and heat your entire city? ;-)

https://en.wikipedia.org/wiki/District_heating

There's one in the Tesla Model Y. Heating and cooling for the cabin, battery, and motors are all handled by a single integrated heat pump system. The part that connects them all together is called the Octovalve.

It's a big advance for electric cars because the cabin heater tends to really reduce range, so making it 3x more efficient with a heat pump instead of a traditional resistive heater makes a huge difference.

Most other electric cars besides Tesla were already using this.

>Why aren't there integrated systems for heating/cooling

Geothermal heat pumps do that.

If you have a geothermal heat pump, you can install a "desuperheater" [0] to recover the excess heat for hot water during the shoulder seasons. It doesn't work so well during the winter, so you need "backup" heat such as an electric element, or a more traditional fossil fuel hw heater (and you might also want one of these as a backup for the geothermal loop depending on where you live).

[0] http://www.geojerry.com/desuperheater.html (sorry, couldn't find a better site)

I had a ground heat pump for several years. It could easily warm a 170m2 house plus warm water. Of the temperature went below -15c or more the electric elements kicked in to boost the pump. I could sit in the living room with a t-shirt on and not worry about heating expenses, it was very cheap to run.

Geothermal heating is pretty standard nowadays in North Europe. Heating the house + hot water is totally doable w/o using an auxiliary resistive heater even when the temperature outside is -20C. Geothermal heat pumps would feature the extra heater (like 9kW) just in case but mine has been turned on only when it overheats the water (60C+ once per week) to reduce fauna build up.

Heat recovery ventilators using heat exchangers have proven to be very successful too. Something like over 90% efficient. Couple that with triple glazing and you almost need no heating.

What I do wonder why there aren’t more in-window air conditioners coupled with heat recovery ventilators?

We have geothermal HVAC. When we moved in we had that water heating setup, but then changed the water heater (natural gas tank). When we did, we asked about hooking up the desuperheater again and were told the energy savings weren't worth it on newer water heating units because of the efficiency. This is coming from a well respected company in the area that specializes in geothermal and heat pumps, and generally has bent over backwards to suggest improvements to all sorts of things in other ways (I also am pretty sure they installed the original system).

Not sure if they were right or wrong, but my experience with a lots of these heating and cooling things is that the real world efficiencies are often different from theoretical values.

Geothermal water heating just barely works out in general because efficiency drops with higher temperature differentials. If you would accept you water at noticeably below body temperature it would be great (though I suspect this is ideal for bacteria growth) efficiency. If you want your water as warm as the minimum recommended temperature by efficiency experts you are already in questionable efficiency range. If you go hotter it gets worse.

Yeah, reducing the temperature on water heaters is a great way of causing Legionnaire's disease.

Given that both the desuperheater and the geothermal both need backup heat, the best approach is to install a small high efficiency gas boiler with 2 zones, one as an indirect heater for the desuperheater (so it'll ensure that the hot water stays hot, but won't run if not needed) and the second zone as a hydronic loop in the air handler to provide backup for those cold nights in the winter that are below the design spec.

Of course, the heat input to your house is a function of heat loss, so if the house is very well insulated and sealed against air changes, regardless of how you heat you'll save energy.

TBH, since geothermal is reversible, in that it does both heating and cooling this makes it even more attractive and efficient especially in the summertime. It should be required in new construction where possible and indeed heavily subsidized to encourage it's adoption.

Years ago, I was convinced that solar hot water heaters were ridiculously efficient and paid for themselves in just a few years.

Since that time, I've come to think that solar PV + an electric water heater is probably a better answer - easier to install, very little relative maintenance.

Now I wonder how solar PV + a heat pump water heater compares (especially if it doubles as a cooler for a surrounding room).

In certain parts of the world (tons of Australia, parts of Africa) literally every single building has a solar hot water heater.

They are fantastic in hot climates, and should be littering the roofs in CA, AZ, TX, etc.

Americans are afraid of the "third-world look" of solar water heaters they know from vacations in Europe

I don't think this is true? Also for what it's worth I've spent time on the roofs of a lot of apartment buildings in the bay area and seen many solar water heaters. Newer buildings and homes tend to just have solar panels if anything, though.

I guess I'm not privileged to have seen that and would mind a setup on my house. I'm in AZ

Not everywhere in Australia, you don't have to fit them but your home needs to meet a mandated minimum '6 star' energy rating. This comes down to everything in the house such as wattage per square meter of lighting, double glazing in windows etc.

The biggest pitfalls here usually with solar hot water is the storage capacity, especially with a family.

You can get hot water for way cheaper using solar hot water than PV. I can’t speak to the maintenance.

That's the thing - I think the economics have changed.

When it was first a thing - solar hot water was expensive and pv was very expensive.

Then I over time the prices dropped. Sites like https:://sunelec.com made me think... I could afford a pallet of panels... or a container!

Also, pv water heating wouldn't strictly require an inverter.

As to the maintenance, I recall the carter vs reagan white house situation.

That's what I did. My water heater is in the basement, and it keeps it dry during humid summers. (I live where we have humid summers.)

In my case, it makes sense because my solar PV is also to run heat pumps for heating and charging cars, and I have a good deal for net metering. Why have a separate hot water system running to my roof when I could just make the pv system a little bigger?

At least where I live, basements get damp in the summer and people have to run dehumidifiers. The heat pump water heater acts as a free dehumidifier that never needs to be drained.

Can you clarify the "never needs to be drained" part?

Most plug-in dehumidifiers (the kind you'd use in a seasonally-humid basement, most likely) are used where there there is no floor-drain, so the condensation is collected in a gallon-or-two-sized bucket that you have to empty periodically.

The plumber hooked it up to the same kind of condensation pump/drain that central AC uses.

My electric bill has gone down over 30% per month after getting one of these. Replaced a super old electric unit. Many states have rebates that an installer can have applied when getting the part from the supplier. For me this cut the whole cost in half. It paid for itself in less than a year. And now my basement is dry and cool in the summer without running a dehumidifier.

You might ask, if these are so great then why aren’t people yelling it from the hilltops? They are, but nobody’s listening.

You are comparing to an electric water heater. I think the cost saving is not much, from a ROI standpoint, if you have a natural gas water heater.

How’s it compare to a tankless gas heater?

Tankless heaters seem like the biggest over promise household tech I can recall in the last decade or two. I have not found over that I would even come close to breaking even on when replacing either of the water heaters in my house.

Tankless heaters heaters are great if you live in a small flat or don't use it extensively (living alone, half of the time taking the shower at the gym).

Currently, in my flat there is only district heating which is way cheaper (lower cost, no maintenance). It's really great, should be the default in high density areas.

Natural gas is the significantly cheaper option in my experience with residential and commercial properties, if there is a utility providing a line to the property.

It would be neat to combine a heat pump (water heater or general heater) so that the outdoor coil (cooling down the air) is put to good use instead of being wasted cold. For example the cold coil could be cooling down a fridge or freezer.

I'm not sure how feasible it would be in practice. There is an advantage in having appliances that are independently serviceable and replaceable. But then again one heat pump system cooling the fridge and heating up water is simpler and less likely to break than two separate systems (one for the fridge, one for the water heater.) Price-wise, however, the labor costs of installing one physically larger integrated system are probably high than the labor costs of installing 2 smaller systems. So many tradeoffs...

The big issue is timing: hot water, fridge use, and home heating would need to be well synchronized to take advantage of this. I.e. you don't necessarily want to make your fridge colder just because you happen to be heating water. The fridge and temperature is set so your lettuce doesn't freeze and your hamburger says solid. Your water heater turns on because you took a shower. You would need to store the thermal energy (a block of ice, perhaps), but this adds complexity and cost.

If the link was optional, so they could either share heat movement or discard waste heat, then there’d be plenty of room for an algorithm to sort it out.

Maybe you can pipe all your heat and cold to central locations and have some kind of heat broker. There’s also a lot of heat in your attic.

perhaps maybe in a large tank of a thermally dense fluid.

But if the link is optional (i.e. no storage), it's unlikely the timing works out often enough to justify the increased complexity or cost. (E.g. if the time overlap of water heating AND fridge cooling is 25% (which seems pretty high to me), you'd only get that percentage of the energy savings.

You don't need to be very optimal to save energy. Your hot water heater is a very good buffer of heat as it stores a massive amount of energy and you don't care if its a few degrees warmer or colder than its set point. In some modern homes the hotwater heater runs far above safe delivery temperature to prevent various issues and is mixed down to a safe temperature elsewhere in the plumbing (either at point of use or in the outlet of the water heater) so the water temperature is even less critical.

The biggest impediment to a system like this is political, as appliance manufactures need to be on board with it, when they have 0 incentive to do so, as their expensive refrigerator becomes a cheap insulated box with a light.

>In some modern homes the hotwater heater runs far above safe delivery temperature

Is this a modern feature? It has been this way for as long as I can remember.

Its complicated, as at first you ran as how as you could to maximize the amount of hot water you had, then there was a period where it was seen as more energy efficient and prevented burns running at lower temperatures. "Modern" practice in this case started somewhere around 1970 where you have a termostatic valve (also called a Tempered Water System) to regulate the temperature of the resulting hot water to non-scalding levels.

Not sure if it's a modern feature per se. But if you have a tankless heater, you can set the temperature to be a little bit above the hottest water you require. If you have a heater with a tank, you need to keep it hot enough to prevent bacterial growth, specifically those that cause legionnaire's disease.

I've seen systems with a tank, heat pump and solar panels, where the system automagically drives up the temperature to kill bacteria every once in a while. Supposedly that's more efficient than keeping it hot all the time.

I think it won't be so bad if only there were some standards. ie. a hot loop, a cold loop. And appliances can just use the standard sockets to hook into these energy sources/sinks.

I can imagine having modular heat sinks apart from the heat pumps which your various household heat pumps could tap into: a warmth sink your cooling devices dump to and warming devices draw from; a coolth sink that does the reverse. It would likely be expensive and you'd need a way to dump the surplus of either outside the building, but I don't imagine there would be much maintenance cost. You wouldn't need moving parts, just a liquid to move heat quickly within the sink via convection. Or maybe a chunk of aluminum would do.

I think that’s why heat pump water heaters are particularly popular in places that predominantly have A/C loads.

In cold country, the « inefficiency » of resistive/combustion hot water heating is still household heat. Just pricier/less efficient than your (typically) natural gas furnace.

In cold countries a typical new installation will have an air-to-water or ground-to-water heat-pump for heating with an integrated hot water tank (actually more like a warm water tank for efficiency reasons). Hot water is a considerable fraction of energy cost in a well insulated home and reducing it many-fold by the typical COP of a heat pump makes a lot of sense.

LG makes a multi-zone mini split system that can use the waste heat from air conditioning to heat water.

https://www.lg.com/global/business/hot-water-integrated

The thermodynamic efficiency of the heat pump is higher the higher the temperature of the cold side, so at least in places where the outside temperature is warmer than the fridge or freezer this wouldn't be a win. This is why you can improve the performance of a heat pump by having the outside circuit run under the ground where the temperature is warmer.

There's also the point that the fridge/freezer is already a heat pump dumping its heat into your house.

Right could we focus that? I'm not sure how much heat it is but I dont like the idea of the fridge just dumping heat into my kitchen while the air pumps push cold air into the same room

The cooler your kitchen is to begin with, the less heat the fridge needs to dump.

I've always wanted to see what could be done to unify all sources of temperature change in a house to a central compressor.

fridge, dryer, water heater, forced air.

Bonus points, bring the sewage line into the fold, heat exchangers can extract heat off of hot water in the line from showers/baths in the winter, and dump heat into the line in the summer from the hot side of the compressor.

I visited a house years back that captured back hot water heat from the shower drain. Hot water going down the drain went through a pipe wrapped with a spiral pattern of other pipe (and fresh water from the hot water tank circulated through there). Don't know how efficient it was, but it was pretty cool to see as a working system.

The keyword is "drain water heat recovery". I don't know the efficiency, but you can buy one for about $600.

Approximately 50%.

Nice, a turbocharged shower.

Here in Canada recovering heat from the drain can be used as part of energy efficiency code requirements in new builds.

They can recover quite a bit of heat, around 50% depending in inlet and outlet temperatures. Pretty good for a fully passive technology that has no maintenance or moving parts.

It does require a lot of copper, so the parts are about $1000 but it's a really easy install.

Those things are neat. I always wondered why they were wrapped around vertical pipes rather than horizontal, because intuitively it seems like horizontal would be better, but that's not the case. I looked it up and it's because falling water in a vertical pipe will cling to the pipe wall, while in a horizontal pipe it will just sit in the bottom. It's obvious in hindsight, but I've never thought about the physics of water in a vertical drain pipe.

This, and blockages...

I've seen a design which exploits this by having the waste pipe flare out enormously - imagine two squat cones joined at their circular faces. You get loads of surface area for heat exchange, with slower flow across it, and no chance of blockage.

This seems like easily the biggest win available to most homes, at least in the UK.

Modern building regulations mean that new homes have to be so well-insulated that heating requirements are small. We have a lot of old housing that was not built to those regulations; some of that has been refitted with insulation, and the rest should be.

Whereas the heat that goes into hot water just goes down the drain, even in the most modern homes!

This is a big deal. When I moved into my current apartment, the thermostat had two settings, "Heat" and "EM Heat". I didn't know what they meant, or what the difference was, and I never bothered to ask. But then one month by mistake I set the thermostat to "EM Heat" instead of "Heat". And I got a $300 electric bill instead of my usual $80. "Heat" means heat pump, and "EM Heat" means emergency heat, which means direct heating, which as the article explains requires several times more energy. I won't forget that again.

Yay for another descriptively named controls on an appliance. What did people designing this think? I know it's probably in the manual. But there are people from whom you can't expect reading the instructions - not because of "fuck the manual" attitude - like guests who live only temporarily.

Would a more descriptive label save them $0.01 on ink or what?

Heat pumps are really amazing and can be used both for cooling and heating with the same hardware. If it wasn't for natural gas they would make sense for many American homes

https://medium.com/hackernoon/the-magic-of-heat-pumps-fd2721...

*if it wasn't for cheap natural gas

Gas is super expensive here in Australia and I plan to try and put 10kw solar on the roof next year. Our hot water is currently gas but I would like to move to electricity. The solar will take 10 years to pay off, I expect adding this to the mix would take another 10 years.

10kW on the roof and a Sanden heat pump hot water set to only run 9-5. I get credit from the Energy Australia for all the summer months which I spend on on the AC heat pump in winter. 25 year warranty on the panels and 20 on the micro inverters. The economics stack up.

Sanden do seem to be the recommended option for this. The problem is if you have a functional gas, the economics rarely stack up to change. If I knew for sure the Sanden would last 10 years yes, but unlike very simple gas water heaters, heat pumps have a disturbingly high failure rate.*

*At least that was the way it seemed from my research, similar situation 6.66kw solar on roof, functional gas hotwater. We do have both Gas and Heat pump house heating/cooling. Heat pump is much cheaper, gas is much faster, even running the largest size possible ducted heat pump split system. I have the gas warm the house from 6am to 8am, then heat pump take over for the rest of the day.

My Daikin is near instant, even when near freezing outside. The compressor is yuge though, so maybe that’s why.

Daikin RXYMQ6AV4A 2 x Daikin FXMQ80PAVE

Also check out https://brighte.com.au/ for an interest free loan for this stuff. backed by Michael Cannon-Brookes.

I have a AO Smith hybrid water heater for the last year and half. Seems to work. Made sense in my case because I wanted to move water heater from the house to the garage. Using a hybrid unit meant I didn't need to plumb gas and figure out how to install a vent.

My suggestion is when you get your solar system installed have the electricians run a 30 amp circuit and disconnect to the water heater location. That way you'll be ready to go. Otherwise you can get stuck if you current water heater dies. You'll be basically forced to replace it with a new gas heater.

Also I saw a youtube video by a off grid nut talking about installing a heat pump water heater. It worked, the only problem it had was the AO Smith unit he was using would test it's heating elements on startup. Which would overload his inverter. I think he fixed that by getting higher resistance heating elements. Otherwise the current draw in heat pump only mode was 300 Watts.

They even beat natural gas on operating cost for many installs these days:

Gas Furnace: 1 Therm = 29.3kWh, Cost $1.5 (at least where I live), Furnace efficiency = 95%. Cost per kWh heat delivered = $0.053.

Heat Pump (COP=5, EER=17): 1 kWh = $0.14, COP =5, Cost per kWh heat delivered = $0.028.

Heat pumps are quite a bit more expensive to install though.

That depends on the cost of electricity, which varies widely across the continent. I ran the numbers a few years ago for central Ontario (napkin math), and natural gas was 2x or 4x the cost (I can't remember). Anyway, definitely not worth it, especially since it falls back to pure electric heat when it can't keep up. And the house is heated with NG anyway, no point in making that energy transfer even less efficient.

(NG fireplace heats the air, air heats the hybrid water heater coils, which heats the water via refrigerant and a noisy compressor. Instead of NG just heating the water directly.)

It might solve some of the solar demand problem. Heat water up during the day when the sun is out, and then store that in an insulated tank.

Have both bath water and central heating run off that.

Makes sense for hot water, but with central heating less so. The energy is mostly needed during the months when there is not a lot of sun, over-sizing the solar collector is financially untenable, as is large enough insulated storage to cover months of heating.

That's already a thing, they just skip the intermediate steps and run the water through black pipes in a sunny spot.

Black pipes are great, it would make some interesting calculations to compare:

Pipes vs. PV taking heat pump characteristics into account, whose efficiency depends on climate. Installation costs, maintenance costs. The Pipes compete for real estate space against the PV, so if pipes are more efficient, does it off set the lost electricity (that would be more expensive, but cheaper than from the grid, but only when it's sunny and you can use the appliances at that time, unless you have a battery which is more capex, so does the interest/repayments on that cost get offset by using electric 24/7). Etc. Etc.

It might need some ML to figure out the best solution. And by ML I mean linear regression.

I put in a Sanden heat pump to replace an old electric gravity water heater 1.5 years ago. Based on power meter data it uses 30% of the energy of the old system on average. This is probably understated as hot water consumption has gone up as the new system and new pipes increased pressure and flow. I say on average as there is seasonality to the energy consumption. I live in a temperate climate, no snow.

We run it at night to take advantage of cheaper separately metered electricity rates ('controlled load'), it could be run even more efficiently during the day, but at higher cost. This and replacing the old gas ducted heating with reverse cycle air conditioning has allowed us to stop using gas, saving the fixed $~30/month service charge. Eventually the additional of solar will further increase our use of renewables.

I do not understand why anyone uses water tanks at all. The tankless or demand-type water heaters tend to be more energy efficient, take significantly smaller space, less parts, and have been in use successfully since the 19th century. Am I missing something?

They take longer for the water to heat up.

And a heat pump is going to beat it hands down.

I don't understand. One of them takes hours the other one produces hot water as soon as you open the tap.

There is a small "spin up" time to get everything hot and hot water pouring out. This is pretty minimal IMHO, and dwarfed by the amount of time it takes to get cold water flushed out of the pipes. Recirculating systems exist to prevent this problem- for tank/tankless systems- but according to some have drawbacks around increasing wear on your pipes.

I have a natural gas tankless system and find this to be a non-issue.

Energy storage. A tank of water can be used to store and release heat from a multitude of sources. Compost, wood, solar, wind, electric, heat pump, gasoline.. The best part is hybrid sources. Couple a wood burner to a solar heater and a heat pump and run the pipes through a fireplace as well. Combined with an intelligent mixer you can heat up your shower and tap water and your house.

I don't know if this is the reason, but one potential advantage of tank water heaters is the ability to use off-peak power. This can be a big cost advantage, and even if it's less energy efficient it can theoretically be better for the environment by allowing water heaters to act as distributed renewable energy storage. At the moment, though, the efficiency savings probably make tankless water heaters a bit more environmentally friendly.

From a grid-optimization point of view a hot water storage is almost as good as a battery. You can "charge" it whenever unreliable local energy sources (wind, the solar panel on your roof) are producing in excess. This helps to consume electricity more locally, and reduces the losses and infrastructure required to transport electricity.

Apparently tankless water heaters draw something crazy like thirty kilowatts, which is more than the rest of your appliances combined and probably requires a landlord to agree to rewiring. Maybe if you have a natural gas supply it's more practical.

This is also why it's rare to fast charge an EV at home—that can top fifty kilowatts.

If you need 10 liters/min of hot water, got an intake temperature of 10C and want to heat it to 40C (hot shower, my gf loves them), it takes about 21kW[1].

If you use a water-saving shower head that only uses 5 liters/min that cuts in half, but still quite a lot of peak energy.

Now you might argue that you only use it for a wee bit while you shower. And that is true. However here in Norway they will soon introduce a peak demand pricing element on the electricity bill, which means you'd likely end up paying a lot for that instant heating.

In contrast, showers are typically taken in the morning, so the water heater tank could get nice and hot during the night when electricity prices are low, and then kept off during the day.

[1]: https://bloglocation.com/art/water-heating-calculator-for-ti... (Water Heating Power Calculator)

Natural gas tankless exists: https://www.homedepot.com/b/Plumbing-Water-Heaters-Tankless-...

I have this in my house.

Electric tankless water heaters draw a massive amount of power. A water heater with a tank is actually quite insulated and efficient. If I am not home and basically use no hot water it can go days without dropping more than a couple degrees. With the heat pump I think I spend about $7 a month on my heat pump water heater.

My concern with these is always the noise. The compressor on there has to be fairly noisy.

There's a compressor too on your fridge you know...

It's pretty annoying too, and so does my air conditioner...the range of noise seems quite wide.

Mine hums like a fridge. Luckily, its straightforward and normal for the heat-pump to be outside or in a garage or basement, so the sound isn't in the living space. Its like: who would want a window-mounted air-con when they could have one of those white boxes up on the roof where nobody hears them instead?

They are a bit noisy, but it depends on the location for your site. In a basement, maybe it doesn't matter as much (and HVAC equipment is likely to be much noisier).

Current models range between 49 and 55 dBA, equivalent to a refrigerator.

This is one of the reasons that heat pumps don't play well with high-density living.

A friend who had a semi-detached house looked into getting air source heat pumps. That would have involved a big fan unit sitting just outside his kitchen window. He couldn't get planning permission, because it would also have been sitting just outside his neighbours' kitchen windows, and it's rather loud.

Ground source heat pumps don't have that problem. But i live in a second-floor flat (third-floor apartment for the Americans) - where am i going to find a ground source? If i run a pipe down from my kitchen, i hit my neighbour's bathroom!

There are several comments on this page suggesting using an outdoor pool has a heat source. Different worlds!

Heat pumps are nothing new. They are not wide spread for a reason. It's weird how old ideas get a new life over and over again. My pet peeve is that these ideas are presented in an overly simplistic way that simply aren't true. "Did you know that you can get free electricity by simply installing solar panels on your roof?" Or "Cut your utility bill 50% by harnessing the power of wind". We know about heat pumps for 100 years. There's a reason why most heaters use gas or electricity - it's cheaper and more simple in installation. There are a lot of enthusiasts who can do things well with their own hands, including sourcing materials, so it's really cheap and simple FOR THOSE FOLKS. But for regular folks these things tend to cost more even for totally proven and technically viable technologies - solar, heat pumps, passive house, water harvesting, etc.

I live in one of the most continuously windy parts of the nation (US state of WY). In the winter time, the heater, a ground source heat pump struggles most when the wind is blowing. I've often wondered if a hybrid heat pump system could be built that drives the compressor and circulation system directly from the mechanical action of a wind turbine rather than first converting the wind energy to electricity, then goes back to drawing from the mains when the wind is still. My thought process is that you would lose energy by first converting to electricity, then converting electricity to mechanical motion. If someone out there likes this idea, and wants to pursue it, I hereby release it to public domain.

Here is some information on this concept. https://solar.lowtechmagazine.com/2019/02/heat-your-house-wi...

Could you use one of these to cool your house and heat your outdoor pool?

There are heat pumps for pools as well as hybrid systems. Also extremely cheap to run. For pools, they actually beat cheap gas heaters.

My pump heats my outdoors pool in summer and the house in winter.

Its more usual to have a small heat-pump just for the pool, though. These are surprisingly cheap, considering the premium on all pool parts generally. I mean, a pool roof made of plastic costs 3x or 4x more.

These are relatively common here in New Zealand, but the upfront cost is high and there is more maintenance than a insulted electric water heater. Retrofitting one will never pay itself off so they only go into new homes.

Most homes in NZ use electric water heaters with gas becoming more and more popular. Gas is only used for heating tap/shower water and cooking, not for heating the home.

Considering that hot water does not need to be heated right away, solar water heating (Direct or via photo-electric) with an electric hot water cylinder as a backup for overcast days would result in more reliable and more long lasting system.

Some people have them here, but it is not that popular. Most of the country has a mild climate and so you would still need an electric heater to keep the tempreture constantly high enough to kill legionnaires bacteria (over 60 degrees celcius).

I think over the lifetime of the system money saved in electricity would not be offset much due to installation. Most of the country is run off hydro so not much environmental benefits either.

> Most of the country is run off hydro so not much environmental benefits either.

Actually, the majority of marginal units of electricity come from gas. That means that every extra kWh you use comes from gas, and every kWh you save reduces gas usage. There are few times when the lakes are full and your marginal unit would come from hydro.

The easy way to think of it is that all the hydro is already used up by other people, so your electricity usage comes from gas.

Hopefully NZ gets some large solar generation, since NZ can “store“ it in lakes by reducing lake outflows during the day (I think).

I get what you are saying but that is not quite how it works. The marginal price may be determined by gas, but my electricity in the south island is mostly hydro.

Right now as I write this comment, the grid in the south island is being powered by hydro and wind. Less power is currently being exported north than is being generated right now by gas up North. So if I turn on a heater, it does not mean that an extra couple of kw of gas is being turned on in Auckland.

Right now the total power accross the country is 84% renewable. So worst case if I use a heater it is 16% not renewable.

In any case, electric water heaters in nz are ripple controlled and only heat at the lowest demand. So any electric water is using as much hydro as possible.

> So worst case if I use a heater it is 16% not renewable.

As a choice as an individual: The heater is off. You turn it on. The extra demand you added usually comes 100% from gas generation.

> In any case, electric water heaters in nz are ripple controlled and only heat at the lowest demand. So any electric water is using as much hydro as possible.

Our lakes are like batteries. If you choose to take an extra long hot shower powered by hydro at the moment, but 3 months later the lakes get low (because there is not enough rainfall) then extra gas generation is used 3 months later which matches 100% of your extra power usage due to your hot shower choice.

Reducing your power usage works similarly, in that you save gas generation.

As an individual, your choices 100% affect how much gas is used, because we are assuming others make no change. This is the key to thinking about marginal usage. Marginal economics are critical to understand when running a business too, since it is similarly confusing (and we all naturally make simple mistakes when thinking about it).

There are times when your extra usage comes only from hydro, but it is usually not simple to know at the point when you are adding power usage. Reducing power usage can only ever help, so different.

I have heard too many horror stories about direct solar hot water. Sure it might work well, and can save a lot of money, but if it breaks it can get VERY expensive. I am looking at electic hot water that only heats with excess solar power though, not mains. Saves sending power to the grid and getting paid very little for it.

Interesting, I ran the math a year and a half ago myself. For my less than 10 year old water heater it was well worth the cost. Was like 3 year break even point. I did the install myself though, wasn't bad at all.

I want to pump this cool air into a server closet with an outtake but I'm sure there are problems with that... Anyone tried?

It would probably be more efficient to pump the warm air from the server closet into the water heater room.

Isn't this just a normal water heater?

Apart from the very simplest models that you might install in a small cabin or separate building (direct-electric or maybe gas powered) isn't this is what you'd normally install in a new house for the last 30 years or so?

No, normal heater heats water directly using supplied energy, while heat pump works like fridge or AC in reverse - it pumps ambient heat to the water using smaller amount of energy.

Perhaps in some locations they install it in new houses as a standard, but I doubt it, it is more expensive.

I guess it depends on where you live. In Northern Europe it's been the default for a very long time, but so has triple glazing and a foot of insulation etc (For obvious reasons). Heating is a large part of living costs and a 30% efficiency increase pays off in no time not least because the hot water is used for space heating as well as for household water.

For that reason you'd expect the same to apply for parts of northern USA and Canada.

no, this one uses the same principle of an hvac, to heat the water with around 1/3 of the energy needed with a resistance.

so far, are very common in new buildings, as you can use the same heat pump you use to climatization, to also heat the domestic water.

Yes my heater is a heat pump and it has been for 30 years. As have all my neighbors’ heaters. Because it’s cold where we live and we use it for heating the whole house (hot water for radiators too). I didn’t think anyone in cold climates or even moderately cold (e.g continental Europe) would use a direct heater, at least not if they have hot water radiators.

https://www.youtube.com/watch?v=omivdhxdGv0

Matt Risinger has some approachable videos to building technology for those interested.

I moved into an apartment that has a Gree Versati Pump, and it's super neat because I can control it via modbus and raspberry pi. Electricity bill decreased tremendously when I moved.

In hot climates you can also recover heat rejected from your A/C compressor, circulate water into a tank, and get a bunch of hot water for free.

Some jurisdictions have a rebate program in effect for these. You should look at whether your utilities company has any information on the subject.

For even better efficiency use an Absorption Heat Pump, powered by natural gas.

But they are hard to find.

These make no sense if there's natural gas available. Natural gas is dirt cheap (heck recently it's being given away for free in many places because it's a waste product from oil extraction).

Not true at all. My basement is a muggy swamp in the summer. I have to run a dehumidifier 24/7 else everything molds. This water heater does that as a side effect. Plus, some of us enjoy owning things that are energy efficient, and are willing to pay for it. Enjoy your global warming.

Is your gas burner inside the house?

Here in NZ I have only ever seen them installed externally.

Depending on where you live you can expect a gas line fee of $20-40 a month before you use any gas. Something to consider.

This was one of the factors that led me to replace two 40 gallon gas water heaters (on two separate gas lines, so $60 every month before a single pilot light is lit) with one 80 gallon HPWH.

The other factor was that you have various options to get renewable electricity, from paying your utility to installing solar panels. There is no such option for natural gas.

>These make no sense if there's natural gas available.

It makes perfect sense: burning gas produces CO2 which is wrecking the climate.

We use a heat pump to heat our 15,000 gal pool in FL - we keep the temp at 94° basically year-round, minus a few weeks, and it costs only ~$150-300/mo, depending on outside temp.

Can you tell me more about it? Looking into this now, but in MD. Waiting for an electrician's quote for running 220 V down there. Which heat pump did you go with, how did it turn out and all that jazz?

Gulfstream. It’s been great so far (couple years in)

Thanks much - which power range (BTU equivalent) did you get?

holy hell. thats more cost than our whole house of two adults and two (just) pre-teen kids every month... JUST for the pool. in fact thats more than our bill every two months (AU$400 every two months), and that's our new place which has some 80's design issues that i need to resolve. our bill should be nearly half that.

Yeah, but to heat a large swimming pool to near-hottub temps... not terrible. Propane would be thousands.

Note that 94°F is 34.4°C.

You've never seen energy used until you live in the American South for a bit.

$400/month for a/c and pool in summer isn't unusual and power is cheap too, $0.10 - $0.15 kw/h.

It's jaw dropping.

Why so warm? As well as being energy-hungry it must make hygiene a challenge

No, salt pools do well. We haven’t had any issues over the past couple years. I know 94 sounds ridiculous, and I could do 88, but everyone loves it that warm.

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