Concept

Everything we have done to reduce heating energy/cost reduces cooling energy/cost. Again, we don’t need to live in perfectly temperature controlled homes. We can take a little heat. The Active Area provides similar benefits on extremely hot and humid stretches. But still, we will experience more hot days in coming summers, so cooling is part of the design.

Application

First, if I need AC, I’ll put it just in the Active Area. However, I don’t think we will. Here is what happens first.

In our current home (well insulated, and fairly air tight), we seldom need AC. If it gets to 80 degrees inside, we turn on the AC. With a geothermal heat pump, central AC is very reasonable, so it isn’t the money (last year AC cost about $16.00 for the few days we ran it) as much as our desire to not waste energy needlessly and our willingness to accept less than perfect conditions.

The new house will be better insulated, better air sealed, have no south facing skylights, and will have southern overhangs to limit summer thermal gains. Plus, it will have more thermal mass. Thus, I expect the inside temperature will seldom reach 80 degrees. But when/if it does, cooling will be addressed as a tiered response.

The first tier is low-energy ceiling fans in the Active Area and each bedroom. These will probably be used in the 75 to 80 degree range. Their basic use is pretty straight forward, though I am considering installing timer switches to automatically shut them off after a period of time. This will save energy and I doubt if we will notice the difference in our sleep; if we do, we can turn it on again…

The second tier is to utilize the Heat Management System (a lot like a whole house fan in this application), which will be used after hot days, with cool evenings. It will draw air from the first floor ceiling to the second floor and expel the hottest air from the second floor ceiling through a vent in the attic. In line, low watt fans are used.

The third tier is to circulate moderately cool water through the first floor slab. If I can drop the inside temperature just five or six degrees, the comfort level will be just where we want it. If the circulating water is about 65 degrees the mass will cool to about 70, and I expect we will have very little condensation on the floor (I did install a durable vapor barrier between the concrete and the first floor deck to minimize concern about moisture induced rot). The trick will be to create a ground cooled reservoir and maintain the temperature that maximizes cooling without condensation. One of the beauties of using water is that I have several variables I can manipulate to achieve my desired results: reservoir volume, ground loop length, and floor loop flow rate. I don’t think cooling will be a big issue, so I’m not spending a lot of time now on design, except to have the flexibility in the floor loops to support my future efforts.

Finally, I am installing a line-set for an air source heat pump to the Active Area that heats and cools, just in case global warming has a bigger near-term impact than expected. These are very efficient with SEERs exceeding 22! And they can throw off a bit of heat, which under the right circumstances might be appreciated.

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