When to Use Ground Source Heat Pumps?

[DanJ]

So I am currently working with a team at my University to develop and construct a “house that will incorporate as many aspect of sustainable design as possible. As most people know, air conditioning plays the largest role in a home’s energy consumption, and because of this, we are attempting to put as much development as we can into reducing the house’s need for energy consumption to maintain a comfortable internal environment.

Ground Source Heat Pumps seem to be a more prominent device used to reduce the energy load on A/C units. I have done a good amount of research into, but have not really found an answer to when GSHP are worth the effort or when they are not.

Most GSHP are not used for a single residence; however, there are some cases when it has been, and apparently has been a net benefit. Does anyone know what kind of environmental or geological conditions would make it appropriate for a residence (probably housing around 10 people)? Additionally, when would the initial expense outweigh the savings? And if you know of any other sustainable ways of reducing A/C load, please feel free to leave them as suggestion.

I have seen a condo in NYC that uses a GSHP, but they had to dig as far into the earth as The Empire State Building is tall. That seems like it simply might be more trouble that its worth.

[West_aust]

We use that kind of heating/cooling system at our house (geothermic if that's what you are talking about), even if the initial investment is quite substantial compared to a conventional system, the size of the house is big enough (our house is around 9000 sq feet) that the savings on the energy bills are enough to pay for the system in a couple of years. (even if here in quebec we get among the lowest electricity price in north america)

We don't have any auxiliary AC unit, and never had a problem with the temperature inside, even when it reaches over 30 celsius outside, and there are auxiliary electric heaters in the system in case we need them, but even then, they barely never come in, maybe only when the temp can reach -30 celsius

So my guess based on our experience is the size of the house must be the main factor to consider in whether or not to get one of those system.

[cfr233]

I've done a few life cycle studies on geothermal heat pump systems, for commercial buildings, not residential. All of my studies found that a 300 foot well is enough to handle the cooling load of about 250 sq. ft. of typical office space in northern US climates. Obviously, there is a much greater first cost than plopping in a direct expansion AC system, but the only electricity costs are running the well water pump, the system loop water pump and fans/compressors in the heat pumps. Maintenance costs are less as well. For the situations I have studied, a facility can expect to see a payback of 6-8 years. However, I would think the payback would be significantly higher for a residential application, as there are less people, significantly lower ventilation code requirements, less computers/servers putting out heat, etc.