Is a geothermal system good if we like a very warm house?
GBA Editor| Posted inMechanicalson
We live in NY and my wife likes to keep the house very warm during the winter. As part of a larger renovation I’m considering a geothermal heating system, but I’m not sure if it works as efficiently if we keep the house so warm – would the backup system be on more often than not?
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Replies
John,
Your question confuses several issues. I'll try to address them one by one.
The basic answer to your question is that a ground-source heat pump (the preferred term, since the word "geothermal" is best applied to energy systems that tap hot springs or geysers) can be used to keep your family as warm as you want.
If you want to keep your house at 80°F all winter, it's possible to design a ground-source heat pump system to meet your requirements. Just be sure to tell your heating system designer what your design temperature is. Instead of a 72°F design temperature, you want an 80°F design temperature (or whatever). This may require design changes — for example, a larger heat pump, or a longer ground loop. But it is certainly possible to design such a system.
These design questions really have nothing to do with efficiency. Efficiency is an entirely different matter. Your question is basically a sizing question.
Whether or not your HVAC system designer includes a backup system is, again, a design matter. It is perfectly possible to design a ground-source heat pump system without a backup system. Just size it to meet the load.
Some designers deliberately design a ground-source heat pump system that will NOT meet the home's load. They include a furnace or electric resistance elements to heat the home during very cold weather. The only reason they do this is to lower the initial cost of the equipment.
This raises the question: if you end up with a system that needs a furnace anyway, why bother to pay for all that expensive ground-source heat pump equipment? If these issues matter to you, tell the HVAC designer what you want.
Here's the basic problem: ground-source heat pump systems are expensive, and designers are afraid of sticker shock. So they often design systems that don't quite meet the anticipated load.
Considering all of these issues, I think you might reach the same conclusion that others have reached: your dollars are best invested in envelope improvements rather than expensive HVAC equipment. Improve the home's air tightness, insulation thickness, and window specifications, and you will be able to get by with a much cheaper HVAC system. You probably won't end up with a ground-source heat pump if you go this route.