Geothermal heat pump system

Although the house is using the sun to heat itself, there is a need for additional heating during the cold winter months when the sun isn't shining. For that purpose we installed a geothermal heat pump system to deliver the needed heat with the utmost efficiency. Yes, the system was costly but given how efficient it is, and the desire to have the home completely run by electricity, it was the most sensible option. The house is designed to be convertible to zero energy, once the total energy loads have been determined. ( PV array) The heat pump reduces the amount of electrical energy needed to heat the home.
How does a heat pump work? That is a sum what complicated answer, but the gist of it, is that it moves heat out of the ground and transfers it into you house by using a refrigerant, compressor and an expansion valve the system extracts heat out of the ground exchange while in the low pressure cold side of the system. Not the simplest thing to understand, how you can move heat efficiently even at temps as low as 32F, but it really works and works well. The other component of the system is the radiant floor slab, which allows for low temp water for heating. Once you have reduced you need for heat through super insulating and air sealing the systems cost is dramatically reduced. For this house we purchased the smallest heat pump that we could find, that would not only provide heat but also provide cooling.
Here is where we stuck our necks out. Not many people try and cool their homes through a radiant floor and there are several obstacles to doing this. First of all most houses require more cooling because the are not super insulated, radiant cooling has a limited amount of Btu's it can deliver. Another major obstacle is humidity and condensation which can accumulate on the floor, if you have rug, wood or vinyl this could be catastrophic. We have installed a whole house dehumidification system that can reduce the humidity in the air and also reduce the demand for cooling. You feel cooler when the humidity level is lower ( it's not the heat it's the humidity) reducing the need for cooling. But when there is a demand the humidity level can reduce the dew point and reduce the chance for condensation. Another part is the ceiling fans which may reduce the need for cooling or at least help to move the cool air off of the floor and circulate it around the room. If we do get condensation on the floor, it is not a major problem. The finished floors are stained concrete, so they won't be ruined if it happens and they won't hide the problem under the rug, making it easy to identify and rectify. Here is a video showing the heating and cooling system.



The closed loop, horizontal ground exchange system was shown on a previous video and gives you an idea how the ground exchange is installed.

This is one feature of the house that has been gaining in popularity in the last few years. It makes your energy cost less susceptible to the fluctuations of the fossil fuel market. Electricity cost do not rise 100% in a few months like the oil prices did over the last year, and enables this house the ability to produce all of the energy it needs to maintain itself. To make the final leap to zero energy is a costly one and given the inefficiency and cost of PV panels at this time it is not the most cost effective approach. However I do believe that PV will get better and the cost will come down, to that end an electrical chase was run from the attic space into the utility room for future use. The roof line was designed to maximize the solar gains and make use of all potential solar energy that is available on this site. Hopefully one day soon, the PV manufacturers will make a panel that is at least 30% efficient and costs less than the house itself. At this time the cost to install PV panels that would produce all of the homes energy needs would be between $40-50,000 and would take the full life expectancy of the panels to pay for itself. Not there yet!!!

Tom Pittsley
ecobuilder@aol.com
www.eebt.org