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Comment by cycomanic | Hacker News Reader

We just build a house on the west coast of Sweden and we initially considered both a ground or air heat pump. Essentially our builder said with modern houses and heatpumps going for the ground heat pump was really not worth it. Their efficiency gain only becomes significant at outside temperatures below 10 deg C and there were just not enough days of such low temperature. Instead it is better to invest that money into a solar installation.

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Göteborg is below 10°C November to March, five months

https://weatherspark.com/y/71566/Average-Weather-in-G%C3%B6t...

in contrast sunshine duration and angle in Winter is frickin low.

sure that guy wasn't trying to sell sth?

I assume they made a typo, and meant to write "under 10°C below zero", Modern air source heat pumps are good to -30°C; the old ones were OK to 0°C:

https://www.heatpumps.ca/articles/best-low-temperature-heat-...

As someone who's used air source heat pumps for years, they were good to around 5C, at which point they would start to ice up and need heat pumped out to melt the ice. They were utter crap if you had any kind of winter conditions.

I'd love to believe that modern ones are better, but its hard to pull the trigger on them after years of suffering.

I currently have oil heat, and love it. Nice hot (not luke warm) air. And if the power goes out, I just fire up a generator and I have good heat, because the blower doesn't take much to run. Having been w/o power for stretches as long as a week during winter, that is a massive benefit over electric heat.

Many modern heat pumps are much better than what you remember. Some maintain their full rated BTU output to 17F, or in the extreme models, 0-5F. They usually output some percentage of full BTU at even lower temps.

The common Asian 'mini split' models also use variable fan speeds to maintain higher coil temps and have output air that is warm enough to avoid the 'luke warm' issue of heat pump coils on 'dumb' air handlers that blow full speed.

That said, for cold environments, a backup is often required to make up for the performance drop at very cold temps without massively oversizing the system. Hopefully, you have your oil furnace coupled to a heat pump or perhaps supplemental minisplit heads. That is the best of all worlds: the HPs can cover 80-90% of the load, only needing the oil for extremes. Oil is likely to hit 5 a gallon this year, like last, so it would suck to rely entirely on it.

Yes - we have a dual fuel system. HP is used when the temps allow it. As far as I can tell, it's not eonomic to run it below 5C, and certainly not comfortable.

Correct I meant to write - 10 deg C

appreciate it, that makes more sense.

Ground source is also just a lot more work, and often has a large part of the job contracted out from your average HVAC tech.

While I do agree that it was true a year ago, I wonder if it holds true for current electricity prices?

My considerations for going with ground source heat pump were:

* the maximum amount of solar that I could install is enough for ground source heat pump, but is a bit short for air source,

* what if the seasonal electricity prices get so extreme, that the grid can't maintain 1:1 ratio for the net billing system anymore?

* what if the global temperature swings become more extreme?

Air pumps have drawbacks outside of efficiency that are also worth considering.

Particularly noise and heat locality. Two properties that combined are not very cosy.

Similar in Lithuania, where buildings are required to be certified to A++ efficiency. Electric floor heating and air to air heat pump (aka split system) is enough. Solar panels are much better value. Cooling in summer is kinda becoming much bigger issue.

For older building even replacing wood furnace with air to water system is enough.

Ground heat pumps provide free cooling in the summer for a very limited amount of electricity as the ground will be at 10-15C (depending on where you live) so you don't need to use the compressor and just make the liquid flow to cool down your house.

It also has the extra benefit of heating up your ground for the winter period.

While that is in principle true, in practice there are quite a few issues. Many heatpumps here are made to heat the water for floor heating but don't transfer heat to air indoors. So you would cool using your floor which isn't very comfortable usually. More importantly because of the above the heat pumps are build for only one directional transfer. If one builds their own system it might make sense to plan for it, but even then it's unlikely that Sweden will become so hot that opening windows will not cool off the house enough. If it comes so far we likely have more pressing problems.

The ground heat pumps are not used in the opposite direction, it doesn't cool down water to the floor but it flows water at 10-15C into your floor. According to the installers I've talked to here in Belgium, all the ground heat pumps devices are capable of doing that.

While this might not be needed in Sweden, it's more interesting further south. I live in Belgium and we had a long heatwave this summer and they predict more of those in the coming years. So cheap efficient cooling might turn out useful here (even if nobody had AC systems 20 years ago)

It would be cool to have a valve to change between a floor heat loop and an air heat exchanger for the inside side of the system.

Of course this makes the system more complicated. More complicated means more chances for failure and higher costs for designing and installing.

Some do wall heating or ceiling heating instead of floor heating. Wall heating/cooling would probably not require two systems.

Not to say you were wrong since in making that choice but with climate change days of extreme temperatures in both directions will become ever more common so so you may have considered it an investment into the future. Of course you may have other problems by then (a reliable source of food for example)

> (...) with climate change days of extreme temperatures in both directions (...)

This sort of take is unwise. It makes zero sense to invest today in domestic systems with the expectation that at some point in the future there will be extreme events a hand full of times throughout the year. The benefit of shaving a fraction of a percent from the baseline outweighs multipercent gains of hypothetical extreme events that happen a few times a year.

And you can always add supplemental later.

When building spend as much as you can on the building envelope (preventing air, vapor, water movement) and insulation.

Those cannot be easily changed at all, but you can relatively easily add another heating or cooling device.

And if you build above code minimums (you should!) be sure to have someone knowledgeable calculate the actual heating/cooling load. If you don’t, the HVAC contractor may assume code minimums and oversize the system.

Or get systems that are entirely variable.

And get every step inspected! Mid build blower door tests are a great thing to do (right after the air seal envelope is up).

> And you can always add supplemental later.

Great point.

Investments are made based on expected returns on investment, and we're free to postpone them until they make sense.

Spending money hoping to bank on the occurrence of unexpected outcomes simply can't be justified.

> Spending money hoping to bank on the occurrence of unexpected outcomes simply can't be justified.

I would have agreed a decade ago, but in the one year our house has been standing, it has endured two 100 year events (a heat wave and a rain/windstorm).

We overpaid about $1000 to go one size up on the (variable) heat pump / AC and $10-20k to oversize + harden the solar / battery.

It has been worth every penny at this point; the solar kept the fridge, freezer and AC happy in > 100F heat during a power outage. That's $500-1000 of food just for the one event, and outages are increasing in frequency. (Air conditioning was mostly unheard of in this area 20 years ago, since it didn't get hot enough to ever run it.)

My big concern is that we're already eating into the engineeeing tolerances for the wind rating on the house itself.

I do agree that you should consider what can be upgraded later, and put money towards things that are hard to change (insulation, wind ratings, etc.)

the "it doesn't get hot enough to need air conditioning" argument was used to build out tons of apartment complexes in the pacific northwest, say, around Tacoma and Seattle. I lived in Tacoma in the mid-2000s for a summer and it was miserable. And everyone i spoke to about it said "yeah, that's the joke."

You are making assumptions that may be not true. 1. Those events will be a handful, I see no indication of that on the contrary 2. You can always upgrade later. You don't how a system can deal with extreme and you don't that those things will be available later. Maybe they will, maybe they won't.

The same can be said for most insurance products. Whether it’s Worth it is subjective.

> The same can be said for most insurance products.

That's a terribly silly thing to say. Think about it for a second, particularly how insurance premiums compare to the cost of buying/rebuilding a new item.

Marge: I'm sure your insurance will cover the house.

Maude: Uh, well, no. Neddy doesn't believe in insurance. He considers it a form of gambling.

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