Best heat pump configuration to combine with geothermal air system in Sedona, Az?
We are planning on using a geothermal air system to cool the house we will build in Sedona Az (750sqf). We are currently hashing out best heating options and heat pumps are winning our favor. What is the optimal combination of the two systems to keep costs down and efficiency high. We will be primarily solar. We are familiar with the Nebraskan Russ Finch (Citrus in the Snow) system and his 8×8 room into which he pumped underground air (53 degrees F) and placed his heat pump. He did this in the 70’s prior to heat pump efficiency improvements. Also, Sedona’s climate is a far cry from Nebraska and we would ideally like to skip the 8×8 room unless its effects and savings would warrant the extra square footage. Any ideas for ideal/simple configurations? Thank you, thank you.
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Replies
Maktub,
Your question is confusing. You mention a geothermal system -- and most people use the word "geothermal" to refer to a ground-source heat pump. These systems are expensive to install but economical to run (if well designed).
So, the obvious answer to your question is this: If you are going to the expense of installing a ground-source heat pump system, use that system for both heating and cooling. In almost all cases, a ground-source heat pump system is designed this way -- for heating as well as cooling. Talk to your HVAC contractor. Any installer of ground-source heat pumps will understand that these systems can heat as well as cool.
Maktub,
Be aware that the federal tax credit for ground source heat pumps was not renewed. This means an already expensive HVAC system will be even more costly.
After Googling the "Citrus in the Snow" system, I think that Maktub is inquiring more about "Earth Tubes" than ground source geothermal.
https://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/do-earth-tubes-make-any-sense
Thank you Martin, Steve and Andrew. I think my mistake was in calling it a geothermal system. In truth it is a geo-air exchange system that we are planning...big difference...sorry for the confusion. Geo-air systems are extremely affordable and simple. Simply put, you dig a trench 8-10 feet below ground surface and you lay 4" HDPE tubing which is then run into the house. The 53f air thus cools your house in hot weather and also brings the temp up in cold weather allowing a heat pump to easily reach ideal temperatures. The 8x8 geo-air room in the home is kept at 53f so the heat pump can operate off of that temperature instead of a much colder outdoor temperature. So basically we will have air conditioner via geo-air, but will need to marry a heat pump into the system. With the highly efficient current heat pumps, is the 8x8 room necessary? We are prioritizing cost effective and simple systems. Researcher Barry Naef details this technology at GreenCube so thoroughly and after further review, I believe I've answered my own question...at least an 8'x6' room will be worth the benefits. Yes, this technology does stem originally from what was called "Earth Tubes" Andrew. Barry has taken it to the next level entirely though. If any of you have experience with this we would be so grateful for your feedback though.
Maktub,
Here is a link to an article about earth tubes: All About Earth Tubes.
In general, I'm not a fan of earth tubes. They are usually expensive to install and problematic to operate.
I also think it's a bad idea to install the outdoor unit of a split-system heat pump in a 8 foot by 6 foot room. For efficient operation, the outdoor unit of a heat pump needs lots of air flow -- after all, it is designed to extract heat from the outdoor air. The heat pump will perform best -- most efficiently -- if the outdoor unit is installed outdoors, in a location without any barriers to free air flow.
In short, you are complicating things unnecessarily. The engineering challenges facing people who want to heat or cool their home have been solved. You should install an air-source heat pump according to the manufacturer's installation instructions.