Interest in heat pumps has increased dramatically in recent years

Really? I live in a mostly not very well-insulated 200 year old wood construction farm house and I find that there can easily be a 10 degree F delta between indoors and outdoors. I have heat for the winter given northern climate but otherwise mostly just do regulation by opening or closing windows.

My house is also in a forest so the sun doesn’t bake it. That might be part of it.

Not to be really dumb about this (I don't have a heat pump, don't know exactly how they work, but have some interest in getting one) -- is it not possible to shut them off entirely for the fall? Are they hard to restart or something? Is it like the obnoxious car systems that always want to be giving you either heat or cool and just refuse to do nothing when it's nice out?

Can confirm. They are awesome

I think systems like this make sense.

I'm not yet convinced that they are worth 3k more than a pico and a fan, at least as a retrofit.

I read that page, and that sounds like a MERV 16 filter than attaches to a third party fan coil. I can’t tell how it’s any different from, say, an Aprilaire 216 plus its (very cheap) housing, along with smart home integration and a pretty logo, minus the transparent pricing.

Matt Risinger explains how and why he put an ERV in his house in this episode of The Build Show https://youtu.be/OrG7oG8Tvp8. It seems to be the thing to do of late in to help with air exchanges and still meet the passive house standards.

How do these systems cope with various temperatures and humidities? You’ve basically got 4 different modes if your climate zone is diverse enough.

WiFi? Eh. As an ever-so-modest upgrade to the cheap DIY, a Zwave or Zigbee system might be a better choice to integrate with a variety of other things (like thermostats and temperature/humidity sensors.)

Presumably you're doing this to pull in air from the outside using negative pressure? I heard this approach isn't optimal because negative pressure means that you'll be pulling in air through the various gaps/crevices in the walls, which is dirty and might have contaminants like mold.

This should not be done because it will draw outside air through the walls of the home leading to moisture problems.

Look at dew point or some absolute humidity measure instead. As air gets colder, the amount of water vapor it can hold (the denominator in relative humidity) decreases dramatically.

Introducing cold, saturated air to your warm house will not, in general, make it feel nasty and humid.

That’s just because the temperature swings wildly. Water isn’t going in and out of the air.

Cold air holds less water, so that makes sense.

It is like pouring 200ml of water from a 1000ml jug into a 200ml jug. Same water, higher % fillage (to use a technical term).

If you're in a climate where that is a problem, the solution is to use an energy recovery ventilator (ERV) along with your air conditioning to use the conditioned inside air being exhausted to pre-treat the incoming air using an enthalpy heat exchanger.

Heat recovery ventilation (HRV), which uses a sensible heat exchanger, is sufficient in temperate climates but otherwise you need to be able to transfer latent heat also to reduce humidity, so need the ERV.

Yes - these are necessary in houses designed to minimise air leakage, because without them they can end up so well sealed that they do not allow enough air changes per hour.

That's kind of the flipside of what OP is describing. OP is saying if it's colder outside than inside, and you want it to be colder inside, the unit would intelligently just pull in unprocessed (except filtering) outside air.

An HRV or ERV is designed to pull in fresh air without losing heat from inside (or while keeping the heat outside in the summer), by transferring heat between the air being drawn in and that being exhausted.

> - why dishwasher detergent packs are stupid (use powder/liquid)

? I thought that powder and liquid for dishwashers have come out worse on any consumer reports test (at least here in Germany).

I take his stuff with a grain of salt because I found the dishwasher detergent recommendation to be a bad idea.

A while before the TC video came out, I had an appliance repair person working on my fridge and asked him what he thought the best detergent was and he said use powdered, not the packs. So we switched to that.

Not long after our dishes were never getting cleaned. I thought it was a problem with the dishwasher so I took apart the filter, cleaned all the sprayers, etc. but nothing worked. Was thinking we needed a new dishwasher until one day we ran out of powdered detergent but had a couple packs left over so my wife used one.

Bingo! Our dishes came out PERFECT. We haven’t had a single problem since.

Is there any meaningful difference between a heat pump and an air conditioner, other than the direction the heat is pumped in?

Wouldn't it be more accurate to say that an air conditioner is a type of heat pump?

Although to be more exact it's a reverse engine, where an engine is a device for turning a temperature gradient into work, and a heat pump is a device for turning work into a temperature gradient.

In this view air conditioners are a kind of heat pump.

That video: https://youtu.be/7J52mDjZzto

TC have a wonderful presentation, but like all YouTube channels, should be taken with a grain of salt. TC made a fair share of errorenous claims, some of which they addressed in follow up videos (definitely not all). One example they never addressed was in their dishwasher video where they explained how a dishwasher worked (which was good) and then pushed to stop using capsules in favor of soap powder. Using powder requires more maintenance because you'll have to buy special salt and run your dishwasher with it but this was never mentioned in the video. The capsules have this so you don't have to add anything else. If you followed their advice blindly, you could damage your dishwasher. Ask technicians what to use and they'll all say the capsules are better for your appliance. Always trust professionals over YouTube videos.

An heatpump is either an Air Conditioner (which is really jusf a refrigerator) running in reverse, or an A/C with a reversing valve so it can move (pump) heat in either direction, depending on the application. Heat pump driers and water heaters never cool the clothes or the water, but home heat pumps are almost always setup for heating or cooling.

Not true. You can just buy a bigger heat pump if you don't want to spring for insulation.

There is a question around time to pay off though. If you run it one day a year, you may as well buy the cheapest possible thing.

Water can carry heat around a building more efficiently (in power and space terms) than air.

In a heating dominated climate, this can make sense in a new building. (It’s also a good match temperature-wise to in-floor radiant heat.)

In a retrofit situation (such as my house), it also makes sense and is cheaper than running supply and return ducts everywhere.

It’s not as good a fit in mixed or cooling-dominated climates (though they can cool as well, but then you have to insulate the pipes much better to prevent condensation).

In our climate there is simply no need for AC as it never gets uncomfortably warm for more than a few days a year. Air to water is used to heat radiators and supply hot water in lieu of gas or oil fired heating. In other climates air to air is more popular and it can be less complex as you don’t need all that extra plumbing.

With new builds air to water makes sense as it’s no different to installing any type of central heating system.

As a retrofit option an air to air system would seem attractive as the installation is much simpler. Our homes tend to be smaller and there wouldn’t be any HVAC ducting so you would probably only have a since source of warm air with an air to air system.

Not an expert, but the much higher heat capacity (and heat conductivity) of water compared to air is likely one reason. But also, when it’s really cold outside, an air to air heat pump is much less efficient. If you have access to liquid water, that is of course much warmer than outside air.

Water is much more efficient at thermal transfer than air. All of those little brittle fins on the outside, less compressor run time.

It's also better in cold weather for heating as a water mass rarely gets below freezing.

The issues are a water source and corrosion.

Heating with air is less efficient in transporting heat with water. So you either need to move more air or heat it up to a higher temperature. The first one is obvious why it’s a bad idea, the second is a bad idea as at a certain point the dust in the air is burning up leaving a bad smell. So practically you can heat a house with air heating alone only when they are extremely well insulated or in a mild climate. The passivhaus-Standard in fact is defined by heating through air being enough.

Other posters are correct that water can transfer heat more efficiently than air, but they're missing or burying the lede:

The temperature is very stable once you dig down a couple of meters. Winter or summer, it's probably an even 10-20 C (depending on your specific location). The ground has tremendous thermal mass and can act as an enormous heat sink. Your little house-sized heat pump isn't going to vary the temperature very much. You can optimize your heat pump to the specific temp range and dump/draw as much heat as you like year round.

There is also question what is the water in picture. Heat pump efficiency decreases when the temperature delta increases. As such it really does depend is the heating done via radiators or underfloor. As later can be used with significantly lower temperature. Where as specially during cold times radiators need rather hot water. In such cases air-to-air might actually be more efficient.

> Newer heat pumps can maintain very good efficiency under 0°C

Well under 0℃, in fact. The Mitsubishi ones are still at 200% at -18℃ (0℉), down from 300% at 0℃ (32℉). They don't fall to 100% until around -26℃ (-15℉). Fujitsu is similar.

Their capacity also falls at lower temperatures going from 100% at -5℃ (23℉) to 76% at -25℃ (-13℉) so you might need to go with a bigger system in some areas.

Heatpumps are commonly used all over scandinavia. They work fine even with extreme temperatures. Temperatures stay well above 0 Kelvin. So there's still plenty of energy to pump around. Of course with extreme temperatures you need to produce more heat. Which simply means you need a bigger setup.

I don't understand how that conclusion follows from the quote.

I still think "putting something warm outside to chill in winter before refrigerating" cost less electricity than refrigerating immediately

Because what you said doesn’t make sense

Running the refrigerator requires power. Is that power usage more efficient than not running it and relying on another heat source?

Parent is right, with some assumptions to be made explicit. Considering the reactions this deserves more explanations ;)

Let's say that the heat energy of the warm thing is "E" and the outside and fridge are at same temp for simplicity. Let's also assume that the house is not heated using a heat pump.

Consider the two cases:

1) The warm thing is put into a fridge. It's a heat pump, with coefficient of performance C. To cool the thing the fridge will consume E/C, and E will be released as heat inside your room. So you paid E/C of electricity to get E Joules of warming in your home;

2) The warm thing is put outside. The energy E is wasted outside, and then the piece put into the fridge with no extra cooling there. No energy spent by the fridge, but no warming of the house either. To do a fair comparison with the same final state, we need to add E joules of energy to heat the house, which will require E Joule of electricity or primary energy (because no heat pump to heat the house).

So to reach the same point, in case (1) we spent E/C of heating energy, and E in the second case. It is indeed more efficient to put the warm thing directly into the fridge, as this will contribute to heating the house with the efficiency of a heat pump.

And if you heat your house with a heat pump of same efficient C, you don't care either way: it's equivalent.

You’re going to have to explain your reasoning to me there.

If your fridge is at 4°C and you put something in there at 21°C it will have to transfer an amount of Joules of thermal energy to the internal environment and then the fridge will have to transport that energy out to the kitchen. The amount of energy depends of the specific heat capacity of the item (J/Kg/K). So to drop the temperature of 1kg of stuff from 21°C to 4°C your heat pump needs to work to remove however many Joules the specific heat capacity determines.

If on the other hand if your item is at 0°C then it’s going to heat up via heat transfer from the other items in the fridge. This means the internal temperature of the fridge will drop. But this means the heat pump will have to work less to maintain the internal temperature of 4°C. It’s not that the fridge attempts to heat the fridge up. The fridge simply works less because no fridge is perfectly insulated so it’s easy to let the temperature rise.

It’s down to cost. The energy rating is subdivided into thirds. An A1 home would have both but an A2 or an A3 will have just one. As long as it’s any type of A rated it’s acceptable.

> depending on local regulations, they may have been able to insulate to a higher standard

Are you implying that some places have maximum amounts of insulation that are allowed for new construction? This seems backwards.

The house was built in 1975. There's about 3 inches of fiberglass batting in attic. One of the first things I'll do after closing is to blow in 12+" of insulation.

In the US at least, high efficiency home gas furnaces bring in their own combustion air from the outside so they don’t bring drafts into the house. They also don’t have flues throughly the roof. The exhaust gas is cool enough that it goes out wherever is convenient through a PVC pipe parallel to the intake pipes.

I do that already, but just for home sanitary water (sorry, do not know the name in English, water for shower etc) with the secondary resistive heating of an "old" (not on sale anymore) Daikin/Rotex M2O EKHHP 300l v3 but I can't do the same for heating: too much water is needed.

Actually I'm looking to expand the system with just a set of insulated tanks (found some on sale 500l/~1kWh/day of dispersion at 60℃ inside, 5℃ outside) and a bigger external heat pump + wood stove (for emergency) to heat the water. It's just an idea because:

- nothing pre-built seems to exists, apparently nobody is interested enough in try this way to save energy bills;

- it not really cheap and DIY style there are many things who can break making the project more an expensive toy than an effective solution.

IF I found something that seems good enough next spring I plan to expand, but it's still a relevant and generally interested issue the fact that nearly nobody talk about the dichotomy between p.v.-powered device needs to maximize self-consumption vs non-p.v. powered homes needs to reduce the total consumed energy: with a p.v. system anything should be designed to run all together at full power as much as possible, so automation to power on and off things quickly and things made to march at very different speed depending on the available power. It's far better for instance in that sense a classic resistive boiler who heat water less efficiently than a heat-pump BUT with a constant load and perhaps not a single resistance but few, to being able to "sum or reduce" the power depending on how much you can get from Sun. While if you do not have a p.v. it's far better to save as much energy as possible...

Some patterns might be common, like running appliance at a dynamic point in time, one depending on the Sun, the other depending on current grid load (and so price). But many others are different. A stupid example my washing machine, with it's eco-mode actually consume less kWh, but consume MORE from the grid because it have spike loads my p.v. inverter can't satisfy quickly enough from p.v. so they goes on the grid. On contrary running an "expensive" high temp washing program my self-consumption is normally 99.99999%

Surely, so far most homes do NOT have p.v. so the biggest market for any appliance is the one who do not count p.v. but is not really expensive counting it. Also it's absolutely not expensive ad ModBUS controls on anything who consume more than 1kW. It does not really change the price. It's absurd not offer such option in most appliance with a significant overprice (let's say 40€ for something that to the OEM cost just 1€).

Heatpumps at least in Austria are the preferred heating method for like 10 years if you build new or renovate. They just work and it’s interesting to see that they are the new sh*t in the US.

My research lead me to exactly the same conclusion. Heat pumps cost the earth if you call them heat pumps, but once you call them an inverter split A/C they magically cost an order of magnitude less (even though it's the exact same tech).

what if we use, as you said, FCUs instead of a traditional radiator?

i understand other commenters are talking about individual air conditioning but that increases the electrical load exponentially because you have multiple units running at the same time... think of the poor wires.

has anyone been crazy enough to preheat the heatpump from solar ? would that even work?

>There are units which exchange heat with water, but typically they won't reach more than 40-45 C°, maybe 50, I doubt 55, so radiators

That's what two heating "experts" told me in Spring 2021 when my gas furnace for central heating needed to be replaced and I asked them wether it would be possible to just replace it with an electric heat pump. "Impossible", they said, your house is not insulated strongly enough and you don't have floor heating, so the outgoing temp will not suffice". It's not true. There are many heat pumps on the market now, and have been since 2020, which manage to deliver 55°C without problem, amongst them, self-contained "monobloc" devices[1] - a box mounted at the outside of the house, which only needs cables and two pipes for connecting to the central heating circulation. With COP values of 3-4 depending on outside temp and outgoing heating water temp. Look at your actual outgoing temp settings (or "heating curve") on the gas furnace. If you never need >55°C, or only need such a temperature on three extremely cold days each year, then a heat pump might be a good idea. Except you can't buy them right now, at least in parts of Europe, for reasons that need not be repeated here.

[1] e.g. this one, which even delivers 60°C: https://www.daikin.eu/en_us/product-group/air-to-water-heat-...

Ya lost me half way, but sounds like you’re describing HRV

Do you know: is this tech useful for hot water radiator/boiler systems or is it just for air?

Oh were the temperatures mentioned in Fahrenheit? Then that makes things a bit easier, I thought they needed 150°C.

Note that the article talks about a different design of heat pump, compared with the common home and industrial HVAC units, for use in industry at that higher temp.

Especially valuable when you have some waste heat from another process.

Probably a good fit for existing district heating systems too.

I completely missed the link to the whitepaper and thought it was just a really bad article.

Does the pdf talk about which working fluids are used? Are there any details at all about implementation?

Yeah that part is a real bummer

If they only have a gas furnace, then they may not have an outside unit currently. Piping a refrigerant line and signalling from where the furnace is to a suitable location for the outside unit may be easy or hard depending on their home.

Of course, if they have a furnace and an air conditioner, it's a lot easier to change to a heat pump and that's it (or more likely, a heat pump and just in case resistive heating)

> Do not burn fissile fuels in your home.

Completely agree; that would be incredibly dangerous and polluting (and probably illegal)!

Buffy had it right, "Fire bad, tree pretty".

It's important for people to know that at least when it comes to heating, "100% efficiency" is actually the worst possible efficiency. That's just thermodynamics. You can only get better than that.

> Typical heatpump COP in Northwestern Europe sits at about 4

:) yeah, when its really quite warm outside, but not quite warm enough that you dont need heating.

as soon as you even get down to 5C outside, you are not getting a COP of 4. Many vendors may tell you that, but well... :) some people were also sold bridges :)

Pretty good assessment, except I think your figure for heat efficiency of power generation is way off. I would expect to convert around 30-40% of the heat energy to electricity.