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Comment by jcynix | Hacker News Reader

Good heat pumps aren't of the air conditioner type. Our heat pump uses two 60m deep drilled holes. Thus heat exchange happens in the ground, which is always more or less 10 degrees Celsuis.

Heat exchange in the house happens through floor heating. So during a hit summer, the reverse capability just pumps the cold water through our floors (controlled for the dew point) and the warm floor water into the ground. That, combined with controlled ventilation over a physical heat exchanger, keeps the warmth out. Or, during cool seasons, the warmth in.

Our heat pump uses about 1 Kwh electricity (from ecological resources like water or wind only) to generatev3 to 4 Kwh of heating. Without producing carbon dioxide. Airflow based heat pumps are less efficient, and more noisy outside, of course.

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> Good heat pumps aren't of the air conditioner type. Our heat pump uses two 60m deep drilled holes. Thus heat exchange happens in the ground, which is always more or less 10 degrees Celsuis.

Good point. The source and destination of heat can be air, water, or "ground source". But it's still all just the same concept as A/C units. Pump heat to one place, using less energy than what it would take to heat it using resistance heating. There is nothing special about ground source heat pumps, except that they're a pain to install in densely populated areas.

All types of heat pumps, unfortunately, often leak. Depending on the type of refrigerant they use, this can be a serious climate concern as well.

The special thing about ground source heat pumps is, well, that they use ground instead of air - and it turns out to be a really important thing because of the temperature differences between ground and air.

A/C or heat pump efficiency is directly related to the temperature difference over which you're trying to pump. If the temperature difference is twice as large, you need to spend twice as much energy to pump the same amount of heat.

Furthermore, the days where you need a heat pump (or A/C) the most are the peak cold/heat days where the temperature difference between your house and the air is much larger than usual. Because of this, a ground source heat pump can do the same thing by spending much less power than an air source heat pump, so it is "greener" - though the installation is more cumbersome and expensive.

However there are air heat pumps which differ from the AC ran in reverse only in how the heat is distributed around the house. For example with warm water in the pipes not just blowing warm air around.

There's no refrigerant here. Our heat pump uses plain water mixed with an anti-freezing agent. Just like the cooler in a car does. And there are control displays where you control all operating parameters.

As for the "pump heat from here to there" ... while we are cooling we are warming the ground below. And as at our place, the ground's consistency keeps the warmth rather local, we reuse it later when we warm our water during the night.

We do live in a densely populated area and about every fifth hoiuse built here during the last 10 years uses a ground-based heat pump. As for electricity use: each house has two hours of "blockage" where the pump is not allowed to run, so that the power lines aren't stressed. That's no problem at all, because all houses are highly insulated and thus buffer rather good.

There is refrigerant there. It is contained inside the system, and only your water mix leaves, but there is still refrigerant inside and it can leak.

That's correct. I was comparing our system to existing systems which directly use a refrigerant sent into the ground loop. Our heat pump itself is a closed system just as a refrigerator, and works indirectly via the water cycle used outside.

Is English a second language for you? I ask not because I am trying to insult, but what you are describing is just called geothermal heat in North America. It can also work in reverse if the air temperature is higher than the ground temperature.

Also, you have your units wrong. Electrical demand is measured in just kilowatts (kw). Actual usage is in kilowatts-hours (kwh) which is just an unusual way of saying joules.

Units are fine. He just said he gets energy as heat in the amount 4 times higher than amount of electrical energy he uses to get it.

It's fine to talk about it in terms of energy as it would be to talk about it in terms of power.

And I'd argue that kWh is exactly the usual way of saying 3600000 joules.

Also name "geothermal heat" for ground heat pumps might be a local US marketing term. In international English geothermal means rather what Iceland is mostly doing. Pumping water into very hot rocks deep below to extract heat. And it doesn't work in reverse because it would be additional work to pump heat into very hot rocks instead of dumping it into the air or into the cool ground 2 meters below the surface.

I don't know anything about Iceland but I am using the definition from energy.gov

https://www.energy.gov/energysaver/heat-and-cool/heat-pump-s...

Geothermal works with either vertical holes in the ground or a big loop spread out horizontally. Neither one is very deep nor does it involve hot rocks.

Ah, geothermal heat pumps is perfectly accurate.

Geothermal heat on the other hand is a wider term https://en.m.wikipedia.org/wiki/Geothermal_heating of which geothermal heat pumps (ground source heat pumps) https://en.m.wikipedia.org/wiki/Ground_source_heat_pump are just a subset.

Energy is specified in KWh here, i.e. we have a metering system installed which states that our heat pump delivered 128024 KWh of heat and the electricity company's metering system tells me that it used 34844 KWh of electrical energy to do this.

Anyway, for one unit input we got about 3.6 units of output, which has been produced with an almost zero carbon footprint, as we buy only ecologically produced electricity.

And yes, English is a second language.

How does a meter compute delivered heat? Computing delivered electricity is easy, but to compute heat delivered you'd need to have adiabatic walls surrounding your house or something like that.

> Airflow based heat pumps are less efficient, and more noisy outside, of course.

This is only true when the ambient temperature dips below the geothermal temperature which depending on your location should make you prefer one over the other.

Germany. Where temperatures dip for some months below the geothermal temperature. Efficiency of air based pumps drops markedly when temperatures reach below 0 degrees Celsius.

And last but not least: ground / water carries much more energy per volume unit than air does. So air based heat pumps would make more sense in Europe's south and less sense farther north.

Modern water/air heat pumps have surprsingingly high efficiency down to -20C. We're running a 10 year old model that has no trouble heating our house down to -12, after which a direct electric helper element kicks in.

What sort of problems did you encounter drilling two 60m deep holes? How wide are they?

We did have no problems as the ground below consists mostly of clay for at least 100 meters. Two times at 60m was a political limit 10 years ago, because at 100 meters "suddenly" mining rules applied.

The tubes are about 100 mm in U-form, drilling mostly is offered in combination with the heat pump. And costs where payed of after about 7 years.

Costs and problems depend on the ground's structure. When I talked with the guys of the drilling team, they told me that problems occur if they work in hill regions with cavernous spots in the ground. That's because the tubes need firm contact to the ground to transfer heat.

Edit: here's an image of the drilling machine in operation: http://www.cynix.net/2008/img_1757.jpg and the tubes are those black ones on the rolls in the front.

Usually 100-150mm wide. You don't do it yourself, you get a company with a drilling rig to come out and do it. Costs around 5k€.

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