Help design my new system please
 

Hello, first post on this site.
I have been reading & learning here for weeks.

I really like this place & want to thank you all for sharing so much info!!!

What I'm doing is trying to design a 2.5 Ton WTW system, using new parts from ebay, Surplus City, etc.

My new house is not built yet & I am designing it to be very energy efficient.
The heat loss calculations look to be about 30K btu / hr at design temperature of 2* F.

Thanks to AC-hacker's thread I am building my coroplast HRV unit.

The building site is in Teller County Colorado about 10 miles W. of Pikes Peak. Great solar location at 8,800' altitude.

The excavation for the house shows that there is only about 2" of top soil, from there down it is decomposed granite, small chunky gravel, much Radon.

So it does not look very good for slinky loops heat exchange. Probably I will put some pipe around the basement perimiter & bed it with crusher-fines to improve heat transfer?

I have bought 240 ft2 of used hot water solar panels + a 1000 gallon fiberglass tank. I will ground mount the panel rack vertically & bury the tank (very well insulated) outside basement close to the mechanical room wall.

I have bought enough of the O2 barrier pex for the radiant floors with pipes spaced 8" OC. + all the needed pumps, HX, valves, etc.

I was my own General Contractor on the house I live in now. I have designed & installed 2 radiant floor systems, learning on each.

As I'm fed-up with mod-con boilers at high altitude, I have bought an 88% Eff. NG Burnham RV-3 cast Iron boiler, about 33K btu output at this high altitude.

It will have long burn times heating the 120 gallon DHW / buffer tank. Heat will be extracted from this tank to heat the floors via the same HX that heats it from the boiler. I have this 2-way HX setup in my current house & it works great!

The solar storage tank will be used to preheat the 120 gallon DHW / buffer tank and the radiant floor directly when it's > 80* F.

In periods of bad weather I will draw the temperature of the solar tank down below 80* F , at which point it becomes usless for heating the floor directly.

From 80* down to 35* I plan to source this to the heatpump evaporator. The destination from the condenser is the 120 gallon DHW / buffer tank.

I have got some Arduino HRV sketches working & will use it to read sensors & control the system. I copied some code from the manifesto thread. Thanks

At this point I have bought a 4.7 ton refrigerant/water GEA flat plate HX, 30 bar, off ebay for use as the condenser.

I think I like this compressor from Surplus City:

Copeland 2-1/4 TON SCROLL COMPRESSOR, VOLT:265, HERTZ:60, PHASE:1, REFRIGERANT:R-22, LRA:58, CONNECTION SIZE:1/2" x 3/4" SWEAT, CAPACITOR:40 x 440, HEIGHT:15", BASE DIMS:7-1/2" x 7-1/2", WEIGHT:58 LBS 2 OZ

I think I will use propane or Mapp for refrigerant. This unit will be built this year & installed after the Certificate of Occupancy is issued, as I don't want a hassle with the building inspectors over a DIY unit.

I need to figure out all the rest, TXV / EEV, evaporator, IHE, superheat, subcool, etc. etc. etc.

Again thank you all.

BBP

How are you going to handle the loop field? What are your thoughts there?

-AC

Have you calculated how much air conditioning would you need during the summer? That would determine if it's worth the extra engineering to make it heat and cool (not trivial on a hydronic system) or if it would be better to separate it. Also note that while 80F water would work for floor heating, it would feel pretty cold for showering. (Not sure what your preferences are - some actually enjoy cold showers!)

Also remember that it's quick and easy to modify stuff on the water side, not so much on the refrigerant side.

This is where it is tough. Geothermal loop fields, in gravel, clay, or other easily dug soils are easy to do. Geothermal extraction in granite is tough - frankly almost impossible.

Three reasons for this:

The first is expense. Each ton of heat pump needs some 200 feet of a vertical column and drilling through granite is expensive.

Secondly, granite does not have the thermal conduction that wet soils have. The BTUs are there, but without good conduction to the pipe, then heat transfer is degraded. This is true even with bentonite slurry injected in well. Solid rock does not have the heat transfer that moist soils have.

Thirdly, because of number two, the vertical heat transfer pipes must be made longer that 200 vertical feet per ton - perhaps double. And for reason one, this gets even more expensive.

I ran into this in New Hampshire with a client (White Mountain area north of Conway). We had to add lots more solar collectors (water type), but we were fighting winter as that location, that far north has minimal sunshine in the winter.

Your location is FAR better for winter solar. My suggestion, to your otherwise excellent ideas, is to add lots more solar water panels for heat collection. Secondly, increase the size (volume) of the storage tank.

Steve

This is going to be a nice install. I must say that if you had issues with mod/con boilers at altitude, you didn't pick the right boiler. Unfortunately, the US made boilers don't have the combustion side of things figured out as well as the Germans do.

On the HP, I would keep a thermostatic valve on the input from any solar assist to the heat pump set at about 20C (72F) to keep the head pressure stable, just in case.

Steve, he has 1000gal tank and at proper ratios, that would mean 200ft2 of panels on the skimpy side and 400ft2 maxed out for that tank. It is plastic so I would not want it to get too hot. Given that he has a boiler for backup, I would stick with what he has and see how it goes for a while.

It would be much more efficient to use a VFD to throttle back the compressor. Or just design the system to be able to operate right to the point where the heat pump can be bypassed. Oversize the condenser and you won't have any excessive pressure problems since water has a lot of thermal mass.

I think that you are making the very same mistake that virtually everyone makes when they consider comfort in a winter home... (including the advice in this thread you have gotten so far) which is that you are already focused on heating a house, rather than retaining heat in that house.

At this stage of the game, since you haven't even built the house yet, you have the opportunity to re-direct the intellectual energy that you now have focused on the heating system, back to the design of the house. 30K BTU/hr @2F is OK, but you can do much, much better.

Every BTU of energy that you can prevent from being lost, is a BTU that you will not have to provide with a mechanical system that IN ALL CASES will be expensive and require some form of fuel and/or maintenance.

Energy retention is extremely reliable, it has no moving parts, you will not ever need to make a service call because your insulation broke down in the middle of the night.

I say that you are wasting your time and everyone else's time at this stage, getting ideas on designing a heating system.

You need to go back to the drawing board in your house design.

You should learn all you possibly can about Passive House design, not only the concepts of insulation, and high performance doors and windows, but the actual details of Passive House construction, from the completely insulated foundation and floor, up through the R60 walls and the R100+ roof, and all of the many details that add up to radically reducing infiltration.

As for radiant floors, if your house is properly designed, you will not require them either.

You don't need to build a pretty good twentieth century house with some improvements and a clever mechanical heating system. You have the opportunity before you to build an excellent twenty-first century house that recognizes the realities of resource depletion, and works with the forces of nature to provide you with an attractive, healthy and comfortable home environment.

Best,

-AC_Hacker

I had a fairly similar situation in Ireland. The ground is layered limestone rock and not practical for a ground loop. After some experimentation I have ended up with an overground heat store that contains about 180,000 litres of clay and rock and is insulated with straw bales. The soil and rock came from the house and avenue excavation as well as two ponds. The store is heated directly with 8 sq metres of solar panels. The temperature is estimated to reach 50C by the end of the summer. The house is mostly heated using a nominal 3 kW GSHP that produces 4.5 kW when water input temperature is 15C. There is also a gasifying stove and separate solar panels for DHW but the heat pump can heat the house on its own if it runs for about eight hours on off peak electricity. There are buffer tanks to mix the water input to the heatpump and to store the output from the stove and heatpump.

The important part is to keep the heat requirement low but DHW will always be needed. In Ireland sun is unpredictable at all times of the year so having an interseasonal store works well. This summer will be the first full heating season, the panels weren't in place until the end of July in 2013 so the temperature only reached 25C.

I like AC's example, persuasive from your main ideas it is giving you a first line of defense rather then a mechanical defense after the build.
following that flavor I suggest to search over some passive house designs find what you really really like and is within your undertaking.

regards