I’m looking for feedback on the system that has been proposed for my new home. We recently moved into a home built this year and wanted a geothermal system, but due to construction delays we decided to move in and have the geothermal system installed afterwards. I now have the specific proposal from the builder for the geothermal system and I want to make sure the plan makes sense before we proceed. Here are the details: * Home is in Western NY with approx 3700 sqft on two floors. Basement is unfinished, but we expect to finish in a few years. * 6ton Advanced Geothermal Technologies DX system with 12 taps * Two 95% efficient gas furnaces (one for each floor) – while I liked the idea of a gas furnace as supplemental heat, having 2 high efficiency furnaces seemed like overkill to me. However, when I asked the GC and HVAC contractor, they said they needed the variable speed blowers to distribute the heat from geothermal system and it was only a small extra cost to get these furnaces. (These are already installed and currently operating as two-zone heating – a thermostat on each floor. However, my understanding is that once the geothermal system is installed, the system will operate as a single zone with two blowers/furnaces because there is only one heatpump.) * Desuperheater assembly to feed hot water storage tank – this water storage tank will supply the house hot water plumbing * Radiant heat in basement floors – may not use initially until we finish the basement, although builder says we should run even when unfinished because upward radiating heat will lower cost to heat the upper floors. * 72 gallon gas water heater – this will feed into the separate hot water storage tank (which is also fed by desuperheater as described above), and also provide hot water for the radiant heat system (via manifold heat exchange). Here are my questions: 1) Does it really make sense to supplement/backup the geothermal system with dual high efficiency gas furnaces? (The ship has already sailed on this, but I want to know if this was done appropriately.) 2) Are the water tanks/flows setup properly? It’s not clear to me that this setup will significantly reduce burden on the gas water heater. I would have thought that the desuperheater could feed directly into the gas water heater (which would directly feed both hot water plumbing and radiant system) without the need for a separate storage tank. 3) Assuming the system is designed properly, how difficult is it to have it properly configured to ensure the gas furnaces and gas water heater are used as little as possible, while supplementing the geothermal system and desuperheater as needed? Are there specific aspects which I should discuss with the installer to make sure it’s done correctly? While I’m excited to be installing a geothermal system, I have some concerns because I don’t think the HVAC contractor has done a system like this before. I don’t want to find out 3yrs from now that the system was designed/installed/configured improperly. Thanks for any feedback/guidance you can provide.
So you will essentially have a 4 stage air handler and a 1 stage heat pump? There is more than one thing about this design that raises an eye-brow. That doesn't mean it's bad, but I would check the installers references very carefully, including visiting an older install site. They might be fine, your description might be confused, but the number one thing we tell everyone that impacts their geo-experience is "dealer/installer" (not the builder). You get the right dealer and design will take care of itself.
Did someone say geo/radiant? I like geo, radiant, zoning, dual fuel challenges and work in NY. 1. There is nothing wrong with using two fuels, it just needs to be done correctly. Since I live in Ohio and every DX geo system here ends up having the dirt eat the copper I tend not to install them, but your and mileage may vary. Rather than mess with two sets of blowers and the accompanying advanced sheet metal configurations, plus the fact that the furnaces and duct work is paid for. I would go with a closed loop water to water unit and add chilled water capable coils up stream from the blowers. That's just me. Water to water and the radiant floors in the basement should be a walk in the park. 2. The benefit of heat pumps goe or air to air is slow and steady as well as the highest efficiency in low temp delta Ts. Got to have that buffering tank, but what about a tank-less finishing system @ 97%? 3. I took care of that issue in 1 & 2 above. Mark
Thanks for response. It's possible that I don't have the right understanding of the system... I don't know what you mean by 4-stage handler and 1-stage heatpump. Are there specific questions I should raise with the installer?
Thanks Mark for the reply. Two follow-ups... 1. Will a magnesium anode reduce the risk of copper deterioration? 2. I didn't fully understand your reply, and I'm unclear on function of buffer tank. Is it standard for the buffer tank to be fed by the geo system (desuperheater) and gas water heater? I would have thought that the geo system would feed the buffer tank, which would in turn feed the gas water heater. But perhaps my instinct is offbase.
I think you should wait to pull the trigger on this until you better understand what you are getting. There are reasons DX are not eclipsing water source geo sales, copper corrosion not really amongst them. These systems do attract newbies however and that's what I smell here. I suggest you follow the shoppers checklist. j
Joe and I do disagree once in a while Joe does not dig very much in Ohio so I will give him the copper corrosion issue in DX systems, that does not change my opinion on Ohio's acidic soil except up near Toledo. I know about the anode systems, but knot much. The chemistry sounds good, but what about real life? Plastic lasts forever, just ask the Pacific Ocean. Digging costs the same what ever one buries. I would say you need two buffering tanks. One for DHW and one for the radiant floors. The most efficient use of a heat pumps energy concentrating ability is to keep the delta T as low as possible. Pick a manufacturer and look at their numbers. The lower the delta T the higher the COP or EER. (To all of you who remember me mixing down water to water heat pumps for radiant floors, please note I can be taught.). A buffer tank allows the heat pump to do its job cheaply. The heat pump will take the tank to say 120* and shut down the heat pump. The house may want a different BTUH transfer rate, the tank allows this to happen. So the outdoor ambient drops 20* and the wind picks up, or a teenage girl, (sorry I know this as all my children are female) gets in the shower, we have a tank full of cheap heated water ready to cover the demand. The tank tells the heat pump to go back to work, but at it's normal pace. The stored heat allows the system to ignore peaks and valleys. My favorite way to heat domestic hot water is with the heat pump and then finish the demand with the second cheapest fuel. To finish DHW one needs speed, so my favorite is gas fired instant hot tankless systems. They almost never run, but if you have a teenage sleep over or invite 12 of your closest friends into your mega shower you will not run out of hot water until you run out of water. Then the energy use is on you. I just allowed you to have hot water. The same goes for radiant systems. Mark
I should elaborate: Where manufacturers' installation instructions (RE testing of soil PH and staying within in prescribed boundries) are followed, corrosion is a non-issue. Certainly areas exist where corrosion is a factor or same manufacturers would not have to set the boundries. Original DXers (late '80s) were by and large already geo pros. Today, band wagon contractors are more attracted to DX as it requires no tools they don't already own (while water source does). Someone new to geo and DX is an unfortunate combination. j
