First off, thanks to the site for being a wealth of information for someone like me shopping for geothermal systems. I've been having a heck of a time getting call backs in my area, so I only have been able to get one quote so I would really appreciate feedback. We are taking advantage of the impending death of our central A/C unit to make the jump to geo. At the same time, we're investing in a community solar project (our panels, their farm, remote net metering) with the goal of going Net Zero. Contractor: A large home performance/HVAC company. Their website has several case studies on geothermal systems they've installed in my area. Inputs: 46 kbtu heat loss, 22 kbtu heat gain System: 1 - 500' vertical loop with 1-1/2" pipe GeoStar Sycamore 5 ton (51 kbtu heat, WF Series 7 rebranded) GeoStar Ashton 2 ton for DHW using a 50 gallon State electric heater for storage GeoStar IntelliZone2 - 4 zones (basement, first floor, master bedroom, other bedrooms) Aurora Web Monitoring Net Price: $28k after NYSERDA grants and tax credits The original proposal called for a 4 ton unit, however its output is only 43 kbtu so with the variable compressor and loop pump I thought it prudent to upgrade to the 5 ton unit. The cost increase was small. I want to preface my questions with the fact that I want to trust the contractor, however they haven't been able to produce loop design numbers which gives me some pause. I've asked all of these questions to them, but while I await a response I would love to hear opinions. At 51 kbtu this is equivalent to a 4.25 ton unit and the resulting loop field is 117 ft/ton. The contractor claims that by going with 1-1/2" pipe the resulting increase in flow will negate the smaller loop field. I've read on here that heat transfer is independent of pipe diameter and larger sizes only help with minimizing pumping pressure. Although they share the same loop field, they claim the hot water unit will have no affect on performance due to the shorter duty cycle. My opinion is mixed on this. I know it's not prudent to size for the full 22 kbtu additional, but is it acceptable to ignore it completely? For the DHW system, the storage tank they specified doesn't have connections to act as a hydronic zone for the Ashton unit, just cold in and hot out. I can't really envision how it would work without 4 connections, cold water in, hot water out, hydronic in, hydronic out.
Looks like they are using the GroundUp Geo design, which by itself is utterly solid (and has been field tested in many settings) and they use GeoStar equipment supplied by John Manning at Phoenix Energy Supply. He is one of the best designers in the Industry, and NYSERDA only gives rebates out after they check out the quality, meaning of your system is not performing the contractor is not getting paid the $10,000 from NYSERDA. The GroundUp design fits for every occasion within a certain parameter, since the variable speed unit is adapting. 1) Larger pipe has slightly better heat transfer due to larger surface area. The key is the higher volume and the continuous draw without pulsing which makes the single borehole perform very well. It might drive the borehole temp further down, costing you a few % on efficiency during peak time, but the average seasonal temp is actually higher. 2) You loop might go down to 25F when both units are running, and the variable speed runs at full capacity. Over all the system will be significantly more efficient. In addition the ground lacks behind (thermal inertia), and only drops to its coldest temp at the end of the heating season (March), however peak capacity is needed normally on the coldest days of the year, typically Jan or Feb, when the ground is still warmer. The borehole design is covering about 69,000 BTU/H heatloss in central NYS climate. We have a single 500ft experimental borehole covering 84,000 BTU/h heatloss load, pushing the boundaries further. So the ft/ton formula is going out off the window. I would not worry about it. 3) Tank: Indeed you have to worry about that the w-w unit turns on, it will pull cold water through the tank and mix it with hot water on the top of the tank. I would be beneficial to have the water going into the heatpump from the tank to be taken from the bottom of the tank. PM me who the contractor is, I can talk to them (we are all friendly here), and I'll call John Manning. Maybe he knows something I don't. But overall your design has been proven to be very efficient. I would not worry. Check out GroundUpgeo.org
My first system was a combo water to water and water to air system. It used a standard water heater for the storage tank. The drain had a "T" installed so water could be pulled from the bottom of the tank to the HP, then sent back to tank via a T in the cold water entering pipe. To me the main draw back is the ports on these tanks are only 3/4". If enough GPM can be sent through the heat exchanger I guess it doesn't matter. I also had a radiant storage tank set up similarly, except the water from the HP back to the tank went into the port for the pressure relief valve. That's how we got 4 connections
Thanks for the great replies. There was some misunderstanding and there is a heat pump loop through the water storage tank, which is what I expected. I have some questions about the control schemes which I’m going to ask the engineer about next week, otherwise I think we are good to go.
The tank is controlled by a simple thermostat, which turns the w-w heatpump on when the tank temp drops below a certain level. The w-w and the w-a (water-air) heat pump talk to each other, since the w-a controls the variable speed circulator serving both heat pumps. As soon as the w-w wants to turn on, the w-a tells the variable speed loop field circulator to go to full speed as long as the w-w needs to make hot water.
Things are coming along, but I have some questions about the zoning. Right now the quote has the IntelliZone2 (comes with a MasterStat) as well as the color touchscreen stat. Reading the manuals it looks like the MasterStat does everything the color touchscreen one does, plus the zone control. Is there any benefit to having one of each in different zones? Zoning wasn’t in the first quote so the other stat might be a leftover. How does dehumidification work when zoning? I understand that the ZoneStats don’t have humidity sensors while the MasterStat and color touchscreen do. If I have 4 zones; one MasterStat, one color touchscreen, and 2 with ZoneStats, will I get dehumification calls from each of the 2 smarter zones? If there’s no cooling call from the dumb zones, will they open up during the dehum call from another stat? The IntelliZone Manual makes it sound like main zone is the only one that has its dampers opened. How about humidification? Our current furnace has a bypass flow-through humidifier on it with an outdoor temperature sensor controlling the set point. I’m being told that I won’t need humidification with geo due to the lower air temperatures but I’m not convinced that’s how humidity works. Our house isn’t too leaky for a house built in the 70’s (0.5 ENIR) but to be honest the humidifier has been installed every winter since we moved in so I don’t know what to expect without it. They said they could reinstall the humidifier if I want it, but the Sycamore manual doesn’t mention humidification at all. I’m also aware that with the lower air temp a bypass unit will be even less effective at making humidity from water than with the gas furnace. If it is possible to get the control working, the same zoning questions apply as with dehum.
The MasterStat is the only device that can control humidity levels in the IntellZone2 system. Choose its location wisely. Typically humidity levels should be fairly homogenous through out the conditioned space. The color touch screen TPCC32U01 can be used as a zone thermostat but dehumidification and humidification functions are disabled. No only the MasterStat. No. The accessory relay on the ABC control board can be configured with dip switches to "Cycle with Comm. T-stat Hum Cmd". I can not address the need for humidification, as I have never installed nor believe it was needed in my case.
Thanks for the great information. I’m hoping I don’t need humidification, and if so I’ll try to track down more infiltration can short of stripping the siding and adding house wrap .
