After a couple months of planning, I'm slightly closer to having my geo installed The main problem is that I don't believe the equipment exists for what I would ideally like installed. For background, I have a ~2700 sq ft stone farmhouse in SE PA, heat loss calculated ~76k, propane powered hydronic baseboard heating for 75% of the house, and 2 propane powered heat pumps in the attic. I've received 2 quotes so far but only 1 of them was comfortable with a hydronic setup. His proposal included: 6 ton bosch water to water 2 air handlers in the attic 1 air handler in basement with new ductwork 1 ductless mini split (this is for a room where extra ducting isn't easily done and I like the mini split for this area) 1 50 gallon hybrid water heater I have a few questions/concerns about this setup. Obviously I'm not excited about using a lower temperature water in the baseboard system but it seems my options are limited with high temp models that offer heating and cooling. The WF only comes in a 7 ton model and I think I'm already oversized at 6 tons. Would it make sense at all to do a 3 ton high temp water to water for the baseboards and a separate 3 ton split for the rest of the house? What kind if cost difference are we talking about? The major benefit of the high temp model is that I believe I could eliminate the need for an extra air handler and ductwork in the basement (this is for the large great room that has a lot of baseboard, so the extra BTUs from the baseboards plus the 2 existing ducts from the attic would come close to meeting the loss of ~21k for that room). Also how would you all approach DHW in my setup? I hear a lot of mixed things about the hybrid hot after heaters.
I don't think a high temp WTW often makes sense. They are not without use, but they have their limits as well. Is there an opportunity to add to the baseboard? More feet at lower water temp = less feet at higher temperature. Instead of ducts downstairs how 'bout high output baseboards if that's what you want. WTA units tend to be higher in efficiency so why not 2 WTA split systems in the attic. Do you not need cooling downstairs? If you put in ducts and a package unit you can eliminate baseboards all together. By hybrid water heater are you talking about a HPWH? We did the math on them and they are overall a plus. If you are going 6 tons of WTW however you might do the DHW with that.
I suppose doing high output baseboards is an option, but I'd really rather keep the old ones (they match the rest of the house and I like the way they look). The extra ducting for that room could only come from the basement, and headroom is already limited there so I'm trying to avoid the ductwork if at all possible (it's a cool looking stone basement). I've basically handcuffed myself with my pickiness to doing the high temp w2w. What I envision as the setup is a high temp w2w powering the baseboards and a split w2a running 2 units in the attic. I guess my question would be does this seem practical and are the costs likely to be significantly more than a large w2w running 3 different units? I'd like to go from 6 down to 5 tons too. For the hybrid hot water heater (AO smith makes a 50 gal), the efficiency is great and the cost is nice, however my concern is durability. It seems lots of people have issues with them malfunctioning. If I'm doing geo a DSH seems to make sense from the efficiency and durability points of view.
Geo/hydronics is what I do. There are some tricks to making what you want to do happen. The baseboard radiation will work at lower temperatures. So will air handlers. I can run the numbers for what the baseboard will put out. How about adding radiant panels to increase the heating out put? What about active chilled water beams rather than fill the basement with duct work? Properly controlled radiant panels can be used for sensible cooling and remove the latent load with the air system. If you use a 6 ton W2W, what is your plan for aux heat? Mark lake-erie-indoor-air-services.net
Another option is the little fan coils offered by thermomatrix - no ducting. Just another zone on your radiant manifold.
Thank you for all the replies. Mark, you did some math for me in a previous thread: The only room that I really feel I need the high temp w2w for is the great room that has 51 ft of baseboard and a loss calc of ~21k. The low temp would give me 8160 btu but when using 140F water I get 16320 btu. There are only 2 small ducts for this room so I think if I was getting 16k+ btu from the baseboards the less than ideal ducts could come close enough to covering the rest. I looked at those thermomatrix products - very cool!
You are literally tanking efficiency across the board by not using more imagination in the great room. Insulate, find a way to bring load down, find away to add radiation, or just put in some electric heat and not bring the rest of the house to a 3 COP because of one room.
Good point. The efficiencies on all the water units seem lower than on the water to air units. Does it make sense to do a 2-3 ton w2w unit for the baseboards and a 2-3 ton split w2a for the attic to gain efficiency? Or is that just a more expensive redundant setup. My other thought was to scrap the w2w all together, keep the propane boiler for the baseboards and utilize a w2a as the primary heat until it gets really cold then use propane.
Oh and stupid question time: when I'm looking at these efficiencies, for a closed loop I need to be looking at the column on the far right, correct?
Now I remember your project, I do not remember screen names well, sorry. You may be closer on the great room than you think. Using Slant Fin again, if we put 1 GPM, at 130*F through your 51 feet of base board we can get rid of 13,260 btuh. Take the flow up to 4 GPM and the out put goes up to 13,770 btuh, hardly worth the cost of the pump and the power it will use for that small of a gain in heat delivered. I agree with Kimko and Joe. Increasing the insulation factor is good bang for the buck. Joe's ideas are also good, and I would flesh the adding radiation out by mentioning radiant walls or ceilings, or some panel radiators the look like art work and work well with low temperature delivery systems. If you can get under the floor you could do a staple up floor. I need more information to do values to pick the best solution. I like multiplicity in systems to a point. How can now three different units be cheaper than a single professionally sized W2W piped to a buffering tank then to what you have and new water coil air handlers? The ducts will still be in the great room and might add enough to keep it warm. The devil is in the piping, but plastic is cheap and lasts forever. Remember the polar vortex? That took most of us lower than design temperatures for a while. How did the existing stuff do during that event? The propane boiler can stay where it is and be piped to the buffering tank for emergency and aux heat. The buffering tank with proper controls will allow the heat pump to provide the sweet spot for your COP. There are several manufacturers making very versatile controls for W2W systems like the Tekmar 406 House Control. I would be happy to lend a hand by phone or in person. SE PA is not that far from NE OH. Mark
Thank you for all the responses. At this point my thoughts are to leave the baseboards alone and have a split w2a installed. This should yield a respectable COP and I can always just use the baseboards when it's really cold. I ran this by my installer and he gave me a nice quote for a 5 ton split. Stay tuned!
