Keeping Cool
Nov 1st, 2008
Your refrigerator works on an interesting principle: When you put a gas under pressure, its temperature goes up. When you release the pressure the temperature goes down. In your fridge, there is a compressor that pushes the gas into a tube under great pressure. That is the coil behind your fridge that is warm. As the gas moves through this tube, it gives of its heat to the room. Then, it goes through a little nozzle into a tube that has very little pressure. The gas becomes cold. That is the coil inside your fridge. As the gas moves through the cold tube, it becomes warmer. And then it reenters the compressor. (Confused? Here’s a better description)
This also how air conditioners work: The warm coils are outside inside that noisy blower thing, the cold coil is in your basement cooling the air in your ducts.
If you have an air conditioner that also works in reverse to heat your house, this is called a heat pump. A heat pump can be made much more efficient (think twice as efficient) if you use the ground (instead of outside air) as a source or dump for the heat. This is known as a ground-source heat pump.
In the building industry, heating and cooling capacity is discussed in tons. A ton is about 12,000 BTU per hour. My facility needs about 30 tons. For each ton, a ground-source heat pump needs a 200′ deep hole. Drilling 30 of these holes (called “loops”) can be rather expensive — each hole costs about $2200 assuming you are buying in bulk like me.
As a result, a ground-source heat pump system will cost about twice as much as a normal heating and cooling system to install. I have decided to spend the extra money for a ground-source heat pump. Here are my reasons:
- It is efficient. The electricity for the ranch will come from burning coal. It seems like anything I can do to keep a little more coal in the ground is a good thing for us all. Over the long run (think 10 years) this efficiency will also save me money.
- It is quiet. Having several noisy blower things outside would totally harsh my mellow.
- It lasts longer. By keeping all the equipment inside, it should run for centuries.
- It makes hot water. When the heat is sucked out of the room, it can be pumped into cold water (instead of the ground) making hot water for showers.
- Tax credits. Remember the 700-billion bailout? It had a clause that gives a 10% investment tax credit for businesses that buy ground source heat pumps. And Georgia gives a 35% property tax credit for businesses that buy ground source heat pumps. Ah, beautiful socialism!
The tricky part is who should design and install the system for me? The technique is new and there is a lot of money involved. Thus, this is an important and difficult decision. I’ve got it down to two companies: GeoThermal Energy Solutions or Coolray. Anyone have an opinion?
Putting the ground loops in drilled holes is the most expensive option. You could save a lot of money by putting them in trenches instead. Putting them in trenches is MUCH cheaper. Also, a leak in a drilled loop is unfixable, whereas a trenched loop can be dug up and fixed if its design or installation prove to include bugs (as all systems do, right?).
Water loops are even better. If you have a body of water (natural or artificial) on site, putting the loops in the water is even better. Putting them in moving water is nirvana. If you can’t put it IN the water, putting it in a trench NEAR the water — and hence in moving groundwater — is pretty darn good.
In any case, a ground loop is best thought of as a water loop — i.e., a loop immersed in water — because it’s the groundwater that matters. Ground loops that are immersed in ground water are very efficient (especially if the groundwater is moving, and therefore constantly carrying away the water mass that’s been heated/cooled by the loop and replacing it with unaffected water mass); those that are in dry soil or bedrock are considerably less efficient.
If you’re using well water for lawn irrigation, you can store the well water in tanks and put heat exchange loops into them, too. As the well water moves through the irrigation system (out of the ground, into storage, out through the sprinklers) it is essentially “moving groundwater” that you can tap as a heat sink/source.
Final point: heat pumps are most efficient when they are saving money at both ends of the loop. For example, if one end of your loop is cooling your training facility’s air (in summer), could the other end be heating a swimming pool’s water? If one end is heating the facility’s air (in winter), could the other end be cooling the pool into an ice-skating rink?
I know about heat pumps because I put in a ground-loop system in at my previous house. It was space-constrained on a suburban lot so I had no choice but drilling. Your facility is likely to be less space-constrained, so trenching or water loops are more likely to be viable.
Now that I’ve seen your site plan, I am convinced that it would be insane for you to drill in your ground loops, when you have all of that open space available for trenching them in, instead.
The Rocky Mountain Institute’s Built Environment group has published a ton of stuff on designing and constructing buildings for resource efficiency. Given that you’re already thinking long-term, implementing their ideas may make it easier to repay your inn’s mortgage – especially if Obama institutes a significant energy-conservation incentive program.
http://bet.rmi.org
Yes, the Carnot-Process, the underlying principle of Heat-Pumps is a thing of beauty. One of the coolest physical principles around. And there is a lot of energy around to be pumped in or out of your house, because 0°C Celsius is still plus 273° Centigrade above absolute zero (or Zero Kelvin).
On the heat source, I agree that doing “horizontal collectors” is more cost effective than doing “vertical collectors”, i.e. drilling holes. You need to understand that you’re not tapping the heat of the Earths kernel, but the heat from the Sun, which makes into the surface of the Earth mostly through rain water. So horizontal collectors, ca. 1.5m deep (depending on how far down the freezing line is) and not under the parking lot (where rain does not penetrate) is a good idea.
One thing is very important, though: the heat source has to be slightly over-sized. You need to ensure that you will never ever extract more energy than it can sustain, otherwise, it freezes up and might get damaged. Also, the heat pump will be more efficient.
The other important thing is on the heat-sink, the system you use to deliver the heat into your house. I assume that you will use floor/underfloor heating? This needs to be planned to have the least temperature feasible. In Europe, we try to go for a maximum input temperature of 35°C if need be and 30°C if possible. Going lower than 35°C increases efficiency significantly. In practice this means to have tighter laid heating coils in the floor. This will cost more, but you’ll get it back over the better heat pump efficiency. You also get more homogeneous dispersion of the heat (no cold spots).
In any case, better insulation means that you will require less energy in the first place, with is always the best thing.
Thanks for your book, Hendrik