I'd love all your help determining the soundness of the geothermal proposal we're considering. Contractor's qualifications and credentials They were recommended by the (independent) company who performed our energy audit. We called several references, who said they did good work. Our electrician (whom we've known for years) says he likes working with them. What is the manual J load, summer and winter design temps? Heating load: 50,684 Btu/h Cooling load: 25,635 Btu/h (19,738 Btu/h sensible) Summer design temp: 94º F Winter design temp: 11º F Size proposed (in tons)/percent of load covered/balance point Size proposed: 3.5 tons % of load covered: 66%* Balance point: 61º F (if "balance point" is the same thing as "building balance temp" on the Geodesigner report) * The percent of load covered has not been explicitly provided to me, but the brochure for the HP says it puts out 33,300 Btu/h at full heating load. 33,300 is 66% of 50,684, so is the % of load covered 66%? Is ductwork and electrical service adequate to support system? The electrical service is adequate. There is no ductwork currently in the house—we currently have an oil boiler with baseboard hot water—so the proposal includes installation of ductwork. (Our home is a 2100 sq ft 2-story built in 1956. It has an unfinished basement.) Warranties One year labor on installation from date of startup. ClimateMaster standard warranty Type of Refrigerant R-410A Proposed loop system Closed loop, 3 vertical bores of 200', grouted at top with Ben Seal Is heat pump 1 or 2 stage? Two-stage. It's a ClimateMaster "Tranquility" 22 (TZ), 3.5 ton. This is the newer model with the internal variable flow pump. Price, rebates and tax credits $30,270 (including installation of all the ductwork). 30% federal tax credit will apply. The price also includes removal of the old heating system, including the oil tanks. Brand, Type (water source or DX) ClimateMaster, water source I think that covers the whole checklist. Other relevant info: We're located in State College, PA. We're planning to set up two zones (one per floor) using a Honeywell zone control board, zone dampers, and bypass damper. The Manual J calcs for zone 1 (the lower level) showed a heating load of 22,338 Btu/h and a cooling load of 9107 Btu/h. Calcs for Zone 2 (the upper level, which due to a couple of additions has more square footage than the first floor) showed a heating load of 28,345 Btu/h and a cooling load of 13,067 Btu/h. 10 kW auxiliary heat The proposal includes a desuperheater with a buffer tank. We opted for an electronic air cleaner and humidifier. I'm planning to set up WEL for monitoring. How does that plan sound? Any yellow/red flags? The main question I have regards sizing, especially on the cooling side. Even in stage 1, the cooling capacity of the unit is 133% of the 25,635 Btu/h cooling load. If only one zone is calling, the disparity will be twice as great. Will we end up with short cycling and inadequate dehumidification? Thanks so much for your input. We're excited about the potential savings and increased comfort, and we want to make sure we achieve those things! Cheers, Brian
On the borehole side of things alone..... I do not like the "grouted at the top with Ben seal" part of your quote. I would prefer to see the boreholes grouted form the bottom up, which is standard practice and IGSHPA approved.
I will put my helmut on and say that designing a system for only 66% of the heating load in " happy valley" is lunacy. Where will the other 34% of the heating come from? How much will it cost to operate the auxillary heating vs. changing the design on the geo and subsequent costs? Even though state boards governing geothermal drilling are slow to catch up, I agree that IGSHPA standards for grouting should be followed- not the local standards. Eric
A couple red flags. Geo systems should not have a bypass damper. It will increase the return air temperature, which will increase the return air temperature, which will increase the refrigerant pressure, which will make the heatpump inherently inefficient. I also have trouble understanding why people propose the TZ 22 model line, which runs about 15% less efficient than the TZ 30. You are spending $30K on a geosystem, and then someone tries to save a couple grant (pre tax credits!), but makes the whole system 15% less efficient...for the life of the system! None of our systems have electronic air cleaners or humidifiers. I tell people that I am happy to put them in later if they feel they need it, no one took me up on the offer yet. They have MERV 11 filters in them, they do a great job. Having 66% of the design load capacity does not mean it carries 66% of the heating load. It means that the balance point is somewhere around 18-20F outside temperature, below that the supplement heat element kicks in and gives shot spurs of heat, but the heatpump still make the majority of the heat. If you count the yearly hours the temps drop below that point, you have about 97% of the load covered. If your load numbers are correct, they would more likely steer me towards a TE049 model.
Moving BTUH with water takes less space from the home. Water is easy to zone with a cheap zone valve and Doc' favorite pump or a differential bypass valve. Using a water to water system it does not matter that you are over-sized for cooling. The chilled water waits in the tank until the air handlers needs it for a cooling call. No freezing coils or messing with air flow. Doc is spot on about messing with the air flow even with an ECM drive blower. His ROI thinking on up-grading the unit is correct. There go the granite counter tops. With a 5-ton water to water unit you could cover all of your heating load and skip the strip heat. Zone with pipe. Skip the Honeywell zoning and buy two two pipe air handlers. What do I know. I was trained as a Journalist, but found I like HVAC better. Mark lake-erie-indoor-air-services.net
to me cost of electricity determines whether one thing fits better than another. first as doc said, the math for pct of load is not as simple as you made it. designing for 95is% means that 95% of the btu's required over the course of a winter are provided by the heat pump. few days are peak load. so that makes the 3.5 ton a good fit. unfortuanately 1/2 tons aren't available in the TE, so while on the surface the heat pump is 15% less efficient, because of zoning and oversize of the TE49 it does not mean it will cost so much less to run that it justifies higher install price, best way to tell is to run the numbers.....or, see if you can mitigate load enough to get down to a 3 ton or the TE038 which is a 3+ton, especially with zones it might fit nicely especially with a designed in floor to floor set back strategy.
Thanks so much for your replies, guys. Thanks for highlighting this, Dan. It reminded me that I had asked the driller about grouting when he came to see our yard. I'm pretty sure he said he'd grout the entire bore hole. I just emailed the main contractor to confirm that. Thanks for the explanation, Doc. Indeed, the "Temperature Bin Analysis" report out of GeoDesigner shows that heat loss will exceed the capacity of the 3.5-ton TZ for only about 45 hours a year. Now regarding sizing and TZ vs. TE. Joe said: Electricity is relatively cheap here: less than $.08 per kWh. Obviously it won't stay that price forever, but given that price it would take 15.5 years of operation for the 3-ton TE to pay back its higher purchase price compared to the 3.5-ton TZ (according to the operating cost comparison report). I could go either way given that payback period. The contractor has said the 3-ton TE should work. After all, the op cost comparison did show it costing less to run, even with the increased use of aux. Could you say more about what you mean by a "designed in floor to floor set back strategy," Joe? OK, now for the part where most of my uncertainty still is. Doc said: And Mark said: I'll start with the bypass damper. Having seen warnings about bypass dampers here on the forums, I'd already asked the contractor if we need it. He said it's likely we wouldn't, and in fact our plan is to set up the system without it first and only add it if we need it. Given that our two zones would be roughly the same size, though, it seems likely that airflow wouldn't be unacceptably high when only one zone is calling. However, it sounds like you guys are saying that in no case should we use a bypass damper. OK, I'm ready to believe you on that. The question of course is how to design the system so that we know there won't be need for it. I think this may connect in with another concern I've had, namely whether a packaged unit in the basement is going to be able to get enough air up to the attic and distributed out around the second floor when the first floor is calling for air too. (I just spent the weekend visiting a relative who has a heat pump in her basement. She has to close off dampers in first-floor supply ducts to get enough airflow to the upper level.) Mark, could you help me understand what you're proposing? I've seen you advocate water-to-water systems a number of times but in my mind I'd always equated that with radiant. Are you proposing we install one split heat pump and connect two air handlers to it? I didn't know this was possible. We did get a quote from another company who proposed two separate heat pumps: a packaged unit in the basement for the first floor, and a split unit next to it paired with an air handler in the attic for the second floor. I liked this concept, but it was a fair bit more expensive. Seems like one heat pump and two air handlers could be a good middle ground, especially if we could skip the zoning equipment. (How would we skip the zoning board, BTW? Would the thermostats communicate with the air handlers, and they in turn with the heat pump?) Thanks again for the help, guys. This is very valuable. -- Brian
Brian: You took the bait so I will try and reel you in. I am sitting in my travel trailer in a state park near Galena, OH, and we are going to install a four pipe air handler as a retro-fit geothermal job. The job has a 5-ton W2W that feeds an 80 gal. buffering tank. The heat pump is turned on and off by the temp in the tank. The air handler will use whatever temp the water in the tank is to make the creatures comfortable. The existing duct work will handle both heating and cooling. Since on this job we will not be able to do all the heating with the heat pump we will use a 4 pipe A/H, you will only need 2 pipe air handlers. A chilled water a/h has a drain to get rid of moisture remove from the living area, there fore two pipes one in and one out. A 4 pipe system has two water coils one that can do both heating and cooling, with the drain system, and one that does heating only and does not need condensate removal hardware. So it has 4 pipes 2 in and 2 out. The photo in my avitare is a manifold on this job. Here is what I would do in your home. Install one w2w heat pump, it would have DHW ability, a buffering tank, 2 two pipe air handlers, one up one down each with their own pump. The a/h units could be standard ducting or HV ducting. I like HV it works better. The stats talk to the a/h units. The a/h units turn on the pumps that draw water through tiny pipes to each unit. The tank tells the HP when to work. The heating cooling change over can go from a simple switch to a Tekmar 406 Home Control. With the system I am proposing, you could add radiant when and where you like. Tiled areas, fancy shower seat to allow shaving of legs and what ever. So there you have my thinking. There is no right or wrong in the HVAC biz. There is only comfortable and not. The cost of real comfort I have found goes well with ROI for same. Like Doc and Joe Hardin, I am never the lowest bidder. Hurry, because if you liked what you read, and you are going to or have broken ground, timing is everything. I hate doing things twice. Mark lake-erie-indoor-air-services.net
I will not install a bypass damper for the reasons Doc describes plus my own summer-centric concerns: sweating ducts, frozen coils. Ways to avoid them: 1) Avoid tiny zones, such as just room, unless you are using really high end systems able turn down below typical two stage low capacity (~67%) 2) Oversize ductwork to smallish zones so they can accept a bit of extra airflow without noise or excess velocity 3) Damper cracking - avoid crappy power close spring open dampers in favor of Belimo or similarly actuated power open / power closed dampers. I like the Belimos because they make it easy to precisely lift the zero stop enough to divert enough air to keep a smallish zone from being too overblown. Be sure zoning is configured so that the system will not kick into high stage if only one out of two zones is active.
Update regarding grouting: the contractor confirmed that the bore holes will be grouted top to bottom. Mark, thanks for explaining what your approach entails. It's intriguing, but it also sounds like it would bust our budget. I'd love to go with something like that, or having two heat pumps instead of two zones. The realities of cash flow dictate certain compromises, though. Curt, thanks for the tips on zoning without a bypass damper. The contractor has already told me that he'll configure the zone controller to stay in stage 1 when only one zone is calling. I'll ask him about damper cracking and your other tips. On the flipside: is it reasonable to expect that a single packaged unit in our basement can get enough air up to the attic to distribute around the second floor even when the supply damper(s) for the first floor is/are open? Any tips for the design of the ductwork to ensure proper performance in that regard? -- Brian
Brian, I don't mean to derail this thread, but I couldn't find a way to message you outside the forums. I will be looking for geothermal quotes for new construction in Centre Hall, PA (6 miles away) from you. I am interested in the subcontractors that you've used and contacted in the area. I can be reached at patmac at psu. Thanks in advance. Patrick
Brian: How the sheet metal duct work preforms is a function of design. Could I build a system that will make your home comfortable without zoning, yes. If you are using air to deliver or remove heat you will need duct work for both floors and each room. The part I am cutting out is the trunk line from basement to attic and the chase built around it. Mark
