Mechanical Systems Planning

Design Requirements:

1. Radiant floor heating. After lots of research, we decided that this was the best quality heat from a comfort standpoint.
2. Summer air conditioning. It just doesn't make sense to not include it in a modern house.
3. High energy efficiency. Money in insulation up front will pay off in the long run, especially if energy prices rise. (of course they will, the question is how much ?)
4. Hot water sufficient for the master whirlpool tub. I have heard of too many stories where people didn't use the tub because of the hassle filling and heating it up.
5. Multiple fuel usage choices (i.e. wood, gas, electric) to be used with thermal storage if appropriate. I like tending a wood fire, and wood is inexpensive on a dollar per BTU basis. Its also good as a backup. Multiple fuel choice lets me decide which is best for me at a particular time.

Design considerations and conclusions:

1. Radiant floor heating- The more we learned about radiant heat, the better it sounded. The Radiant Panel Association web site was a great source of information. I am still involved in discussions in their BBS forum, and I signed up as a member. Warm floors, lower air temperatures, quiet operation, consistent temperatures, good compatibility with alternate fuel sources are just a few reasons. Heat tubes in thin, 1 1/2"  slabs would feel solid under foot, deaden noise transmission, and be the best place to store heat. Since floor heat uses direct radiant transmission, as opposed to air heating to supply energy, the required source temperature is much lower. Most radiant systems could use water as low as 120 degrees F, as opposed to 160  degrees F. for a hot water baseboard or air system. This lower source temperature greatly increases the efficiencies of heat pumps and solar collectors by reducing the temperature difference between the source and load, and thermal storage cells by decreasing stand by losses. Surfing on the net, I tracked down an engineering firm that has good experience with residential radiant design, the Monterey Energy Group. They quoted me a range of 15  to 25 cents per sq.ft. for the design and tubing layout plans. The actual price wound up to be 25 cents, $850 bucks. I supplied the AutoCAD files for drawing blanks. It was probably at the high end of the price range because I specified that they use the minimum tubing spacing (maximum amount of tubing) to take particular advantage of low water supply temperatures down to 100 Deg. F or so.  
2. Summer air conditioning- The design of the house was not friendly in this regard. The attics between the above the master suite and the second floor do not connect because of the height difference. Since the existing first floor already has central A/C, we would need two more air systems for the new construction, making a total of three. Adding a fourth for the workshop would be out of the question. Three DX (direct expansion) split systems with condensing units outside would be expensive, and a lot to maintain. The solution to this would be to use a chilled water system. This would circulate chilled water to the air handlers, which is much easier and cheaper to distribute and move around. A traditional industrial chiller in the 30 ton range uses a cooling tower to reject heat. I only need 5 tons, and a cooling tower would not fit in well in the backyard, although I considered constructing a special fountain for this purpose. I began to consider using a ground source heat pump. There was a lot of useful information on the International Ground Source Heat Pump Association (IGSHPA) web site. Another friend of mine, Ben, was also looking into this recently. His research  into drilling wells found that for four tons of refrigeration, two 300 foot wells would be needed. At a cost of about 10 dollars per foot, this would cost about $6,000. For estimating purposes, if the chiller cost $ 6,000 and the 3 zones are $4,500 the total would be $16,500. The wells would represent 36% of the up front costs. With the three zone floor footage a @ 2,500 sq.ft. this would be $6.40 per sq.ft. (ugh) for air conditioning only. Of course if we went with forced hot air heat, its already included. If a reversing chiller (heat pump) is used, the same unit will also provide hot water for the radiant floor heating. Following this design thread, I got the name of a company that made these RRC (reverse cycle) chillers, the Aqua Products Company from the Radiant Panel discussion BBS, and gave them a call. Their representative, John Sappamaki, was really helpful and willing to discuss my application. Although they did sell reversing chillers for ground source applications (water inside the house, water outside) he strongly recommended using an air source chiller (water inside, air outside). The company claims that their air source systems are as economical, or almost as economical to operate as a ground source heat pump. There are a few interesting twists to their system design. The units are sized for the winter heating load as this will always be greater than the summer cooling load. To enhance efficiencies by allowing this equipment to run at a fully loaded condition, water thermal storage is always included. Preventing short cycling is an another benefit from thermal storage. The system price is similar to the ground source heat pump system, above except for the expense to drill the wells, which then totals to $10,500 or $4.20 per sq.ft. . Adding another zone would be easy and relatively cheap. If I added the workshop someday, which could potentially be a rec. room, the per sq.ft. price would drop to $3.60. I am seriously considering this option.
3. High energy efficiency- This doesn't come cheap. 2 inch pink insulation board to insulate below the slabs and thermal storage is 60 cents per sq.ft. Vermiculite in the cement block cores increases the R value of a 12" block from 2 to 3, a 50% increase. 72 bags @ $9.16 per bag is $670 bucks !
4. Hot water sufficient for the master whirlpool tub- Most likely, I will use an indirect water heater. Instead of using a certain energy source (like gas or electric) the domestic water will be heated by the circulating system water using a tank-in-tank setup. The thermal storage in the system will provide lots of heat for the domestic hot water in a short time to satisfy the filling of the tub.
5. Multiple fuel usage choices

Temporary Heat

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