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Comment by brightball | Hacker News Reader

I have a 2 story house with a heat pump for the upstairs...and I hate it. It causes so many problems that we just keep the heat very low up there so that the heat drift from the 1st floor furnace does most of the work.

When it runs, you can never set it higher than 2 degrees F above the current temperature and if you do that when it's even close to freezing outside the unit will build up a think layer of ice around the casing...which just makes it spin constantly until we turn it off to go manually de-ice it. It's the most hated piece of equipment in my entire home.

Do you have a reference for one of these more effective modern heat pumps? I've been sincerely planning to install geothermal when this thing dies.

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These are the two biggest complaints about heat pumps: one, they blow out air that is only marginally hotter than the room air (unlike a furnace, which pumps out hot air, or a scalding radiator), and two: heat pumps take a very long time to warm up a cold space. If you try to ramp up rapidly, you’ll often trigger the “emergency heat” which is usually electric strip heat and thus VERY inefficient and expensive.

Heat pumps work best when you maintain a room at a stable, comfortable temperature.

You don't want to use a heat pump to blow hot air. You want to use a heat pump for low temperature underfloor heating. The heat is right where you want it, the heat pump doesn't have to work as hard (because of the lower temperature). And everyone is happy.

"Heat pumps work best when you maintain a room at a stable, comfortable temperature."

Right, but for this to be economical, you need to have a well-insulated house, which is pretty much impossible to retrofit. So practically speaking, only newly build houses (and then, only those to the highest energy standards) should use heat pumps for heating. If we go around promoting them for other purposes, they will build up a reputation for being a crappy solution and people will shy away from them. That's my main problem with people promoting them - they often promote them for retrofits.

Groundwater systems are much better. My parents house in Ottawa has one, and it works fine through -30 C nights. There's a source well about 30' deep with a pump at the bottom, and a return well some distance away. That provides a constant supply of water around 5-10 C for the heat exchanger.

It is a complicated system -- lots of valves and reservoirs and so on, but very efficient and doesn't need much maintenance.

I grew up just outside of Ottawa and we had a system like this 20 years ago. I don't think you can get a permit for them anymore because they don't like you moving water from one water table to another because of contamination reasons. Nowadays, it's mostly ground loops being installed. In rural settings where natural gas isn't available, and you have the space to run the horizontal loops, they're a good option.

Worse than that, they won’t allow direct expansion systems. So you need a glycol loop going through the ground which has another heat exchanger to the refrigerant loop.

I wonder how we could work this for an urban setting - could we use the water lines?

It consumes a lot of water, so it'd be expensive if you send the outflow down the drain. If you pump the outflow back into the fresh water supply, you have to worry about contamination from everyone's heat exchanger.

In a dense urban setting, you can heat homes with water heated at the local power plant, either fossil or nuclear. https://en.wikipedia.org/wiki/Cogeneration

There's closed loop ground source heat pumps. It's all very situational as to whether they are practical to install. The vertical ones are more expensive but don't need a whole lot of ground area to be installed.

In my city, about 10% of the district heating load is covered by heat pumps where the heat source is municipal waste water.

Toronto does this for district air conditioning with incoming city water.

I don’t think they’ve bothered to calculate the effects of pumping warmer water into everyone’s air conditioned home...

If we think insulating a single home is bad, image trying to build the infrastructure for that throughout a city.

You could do some heat recovery from the sewer, but it would be a yucky affair - they already tend to clog even without heat sink fins in them :)

Here are some calculations suggesting that the numbers simply don't add up for ground-source heat pumps at urban population densities: https://www.withouthotair.com/c21/page_152.shtml

A similar idea that's somewhat popular in Sweden is to add a heat-exchanger between outgoing sewer water and incoming tap water. You don't need to put fins into the outgoing water, it's simply a piece of regular straight copper pipe, but it's thicker, and the incoming water pipe coils around it a bit.

No need to muck around with fins in the sewage, or trying to convert to electricty, simply heating the incoming water a degree or two saves energy for your water heater.

Yes, we've got this on our shower drain. In this configuration it does better than a degree or two, recovering some 50% of the heat, in fact.

You normally have to drill one of more well holes. If you can't go horizontally you have to go vertically.

Maybe you have a really old one or an ac-unit in reverse? My pump works perfectly well in -15 C and I have no problems with ice.

In Norway most pumps are Toshiba and Mitsubishi. F.ex Mitsubishi FH35.

Heat pumps all have defrost cycles where it'll run like a regular air conditioner to heat up the outdoor coils temporarily to melt off ice build up. It turns on auxiliary electric heating inside in order to maintain heating while it does this. Yours clearly is broken in some form or another, it's either not going into a defrost cycle at all or even a full defrost cycle isn't enough to melt all of the ice and it's building up faster than it can be defrosted. Just call an HVAC company and get it fixed.

that sounds like it needs maintenance. I can't remember what it was but something was causing that to happen our ac unit in the heat and we paid like 200 to get it fixed and it stopped happening.

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