South Carolina Undereducated Newbie with general questions

Hello,
Allow me to apologize in advance for the very long post. I am brand new to geothermal. I am located in the central part of SC. I own a 3000 square foot historic home with minimal insulation. 1800 sq ft downstairs and 1200 upstairs. We have around 10" of blown cellulose in the attic and 6" batts underneath the house in the crawlspace. External walls have only been insulated when the exterior siding needed replacing which allowed me access to install batts with vapor barrier. Otherwise, there is no wall insulation. I am planning on adding additional cellulose in the attic this summer.

We recently had all the ductwork replaced as well as both hvac systems. The installer put in a closed loop system with four 250' long trenches 6' deep. The loops ran out on the bottom of the trenches and returned at 4' deep. The upstairs now has a 3 ton Waterfurnace 5 series split unit (500A11). It has performed well since it was installed at the beginning of December 2021. It runs mostly in stage 1. Two weeks later the downstairs unit was finished. It is a 3 ton Waterfurnace 5 Series outdoor package unit (506A11). Since it was installed, the unit has been running on the auxiliary heat about 1/3 of the time. I kept questioning this and finally after I got an outrageous power bill, the installer came out and installed an outdoor sensor and programmed the unit not to use the heat strips until the outside temp reaches 10° - which should happen once every five years or so here. Since the heat strips were disabled, the unit has struggled to heat the downstairs. The last three nights it was 27, 28, and 30 degrees respectively. Running in stage 2, the unit was not able to reach the 70 degrees set on the thermostat until the late afternoon. We also have an 8 degree difference between the first rooms in the duct run and the last 2 rooms in the duct run. One other odd thing is the waterlines as they exit the ground under the house are actually about 70' or so from this unit itself so they are lying on top of the ground in tube type insulation for about 70' til they reach the unit. (Upstairs unit has the pipes coming up underneath the unit like they should be.) My installer doesn't think this makes a difference.

The installer did run a program to determine the size of the units needed. He knew we had an under insulated historic house and that we will not be adding any wall insulation and added that info into the program. How can we need the same size unit for the upstairs and the downstairs? From the symphony program I can tell that the loop temperatures for the upstairs unit is typically 9 degrees warmer than the other loops. The trenches were filled with the air temperature being around 65 degrees for the upstairs unit and the dirt was dry but the other unit 2 weeks later had a much colder temperature of around 39 degrees and the soil was wet for those trenches when they were filled. Could that still have an impact 45 days later? Also, I've noticed the supply air temperatures for the upstairs unit are usually 10-15 degrees warmer than the other unit. I'm hoping to get some suggestions and education from you guys. My installer has said that worst case scenario we can increase the outdoor packaged unit to a 4 ton and that would necessitate adding an additional 200' trench. He wants us to wait until a cooling season cranks up to make that decision. But if the 3 ton unit isn't capable of heating the space when the temps fall below 35 or so, what does it matter if it can cool the space?

 

There are people much smarter than me here, so hopefully they will chime in as well, but a couple items to verify with your installer:

1) Did they perform a manual J calculation? This is the calculation that the contractor used to size your system by calculating the heat loss/heat gain. I have never done one of these myself, but I don't believe they are perfect as they make some assumptions for insulation and leakage rate, which sounds like you would be on the high side for (less insulation, more leakage). Your contractor should be able to provide these numbers for you and sounds like this may be the "program" you are referring to.

2) Your contractor should verify the heat extraction (HE) from each unit to verify proper operation. This is pretty simple and is done by measuring the pressure differential across the unit to calculate the flow rate and then using that, and the delta T (temperature differential from entering and leaving water temperature at the unit), to calculate the how many Btuh the unit is providing. This can then be compared to the unit specifications to verify proper operation.

What are the entering water temperatures for both units? If you are in the high 30s, than the loop has plenty of margin to go lower, with 30 degrees being a standard design limit for heating. This doesn't necessarily mean that your loop is sized correctly because, if the heatpump isn't pulling the appropriate amount of heat, then your loop temperatures would be higher, but items 1 and 2 above will at least help you verify that the system was sized correctly and that each unit is working as it should.

Where are the supply air temperatures being taken? The correct place to take them is right off the unit. Taking the temperatures at the registers doesn't tell you anything as leaky ducts, poorly insulated ducts, or running through unconditioned spaces will lower duct temperatures. From what I understand, a delta T across the return and supply duct of 20-25 degrees is pretty normal.

As for the lines, I live in CT, so heating is the governing load. My lines remain below the frost line from the top of the vertical well and into the house, where they come through my foundation into my basement. I would expect the same for your setup, but with a lower frost line. Running above ground, even in insulation, seems less than ideal, but others may have a different opinion. As for when they were buried, I doubt that matters. Once the lines are buried, the ground will pretty quickly get to an equilibrium.

 

Thanks for the reply. I'm not sure what he called the program he used to determine the unit sizing. He mentioned adding information such as the storm windows, lack of insulation, age and type of construction, etc. I will ask him if he can give us a copy of the results.

As far as how the unit is running, our contractor did hook up his fancy gizmo to the unit and said that it was meeting the specs. He also has been monitoring it through his symphony connection so he is aware that it is not satisfying the thermostat throughout the night.

The supply and loop temperatures I previously mentioned were numbers I got from the symphony program. I can get more specific numbers after it cools down in the next few days. Today was 75° so I dont have accurate numbers since the system isn't running. I am concerned that the heating season here will be over soon and we won't have enough information to make a decision about the unit's ability to properly heat. I do trust that our contractor will do right by us but I'm still a bit uneasy about the whole situation.

Thanks again for responding.

 

Another item to check is if the heat pump locking out (shutting off) when the aux heat is on? Heat strips are generally designed to supplement the heat pump when temperatures get too low. If it is running on aux heat, the heat pump should still be running, while emergency heat will generally lock out the heat pump. If it is running in emergency, something may be wired or configured incorrectly. You can verify this pretty easily by just cranking the heat (even if its on the warm side outside) and seeing if the heat pump shuts off while the thermostat is calling for heat. The fan will still be running, but you won't be getting any flow through the loop. If it is running in emergency, this may explain the high electric bills along with the high loop temperatures.

With a leaky, poorly insulated house, it may just be that the heat loss is greater than a 3 ton unit can handle. Either way, before making any changes, I would verify that everything is operating correctly.

When you get the heat loss/gain numbers I would also ask for the heat extraction number that your contractor measure and verify for yourself that it matches the published values for the system. They can usually be found on the manufacturer's website or in the owners manual.

 

If I had to place a betI would say your loops are too small.

 

I initially thought that as well, but if loop temperatures are in the upper 30s, that doesn’t sound like an undersized loop

 

Lots going on here. lets try to break apart

More info is better no reason to apologize. You don't have "no" insulation. not great but better than nothing. Air sealing is as important if not more important than insulation. Air sealing eliminates convective heat loss/gain (heat moving via air current) while insulation eliminates conductive heat loss/gain (heat moving through contact of materials). Radiant is a distant third way energy moves - I wouldn't worry about it and focus on air sealing and insulating.

The whole manner in which heat strips were disabled is weird. The way it should work is if unit can't meet thermostat (ie your heat loss exceeds the amount of heat the unit can put into the house), then electric heat comes on to supplement. Tying heat strips to exterior temp doesn't fix this and only causes them to lock out when they are otherwise needed to keep the thermostat at its set point because the unit's heat pump capability by itself can't do that. There could be a variety of reasons why the heat pump can't meet set point - it typically boils down three main things: unit too small, unit not getting enough flow from loop system, loop system too small. Your text suggests both units are on the same loop system so it seems unlikely you have an incoming water temp problem (a sign the loop is too small) if the upstairs unit is fine and the downstairs unit not so great. How is the loop plumbing done - layout, sizing, how the plumbing gets combined, flow centers, etc.? Tends to be lots of problems here with installers as very few understand water flow.

99% heating design temp in South Carolina is between 20 and 30 degrees (See page 102-104): https://www.energystar.gov/sites/de...9 Ed) - ENERGY STAR Certified Homes_Rev10.pdf
So if the system is properly designed for heating, it should be able to handle 27-30 degrees fine. Statistically, you should never see 10 degree exterior temp in your lifetime in SC given the data in that link.

Loop piping above ground sounds like shoddy work but maybe there was a reason based on existing construction that isn't clear here. If its insulated, it shouldn't be a detriment but I would certainly be concerned about physical damage to the lines.

8 degree difference between first and last rooms on one duct run from one unit sounds like a duct size problem with too much friction loss between air and duct forcing most air out closest room.

Knowing nothing about the house or what this installer did, you have two season and differing heat loss/gain to deal with. Link above shows 90-95 degree cooling design temp and 20-30 degree heating design temp. That is quite similar to where I am at in NJ and I am solidly in a heating climate. Its hard to determine unit size without calcs but it certainly seems like your downstairs unit is too small for heating. Why upping the size of that unit requires adding loops is not clear to me - units respond to heat gain/loss in house happening right now; loops deal with heat extraction/rejection into ground over a full year's season. think of your unit as "weather" and the loops as "climate" Although they have a relationship, it isn't direct and suggests the installer doesn't know what they are doing and relying heavily on computer programs/garbage in-garbage out type analysis. Always love the person saying, "but the computer tells me it should be this way" as if their input and understanding of the program and what it is doing has nothing to do with the output. Need more info on the loop setup and how they are connected to the units.

 

Are these units under the house? Ductwork in the crawl space?

2000 ft of loop is not bad, doesn’t sound like both units are not running full out at the same time.

Summer the upstairs will run harder and 1st fl less.

Your climate is close to even on cooling/ heating, a little to the cooling side.

Maybe a different thermostat to better control the aux heat.

 

Bare with me as I i try to answer some of y'all's questions. The photos show the general layout on one of the four trenches and also the manifold setup as the lines from two trenches are combined to come towards the house. Each unit has two trenches (6' deep and 250' long) that come to a manifold which comes to the house at about 2' deep. The lines in the trenches are 3/4" pipe and the main lines coming up to the house are 1 1/4".

The upstairs split unit has an air handler in the attic with the ductwork and the compressor is on the outside of the house. The downstairs unit is an outdoor package unit with all of the components outside the house and the ductwork is under the house. My contractor felt it was too tight to place the unit underneath the house in the crawlspace so he ordered the outdoor package unit.
As far as the energystar numbers, I think they are historical averages but I definitely have seen the temperatures here go to 5 on more than one occasion and it has gone over 107. Quite the range. But I know those numbers are not the norm. Is it accurate that waterfurnace builds these units based on regional weather differences? So a person in SC gets a differently built unit than a person in Michigan?

I have spent a good bit of time (and caulk and backer cord) trying to help the air infiltration for the old house. I figure anything I can do to lessen air leaks is a plus.

In regards to auxiliary heat versus emergency heat, I have actually seen the waterfurnace thermostat go into emergency heat when the upstairs unit was first installed due to a fault. When it went into emergency heat, the thermostat diaplay actually turned red. We have the same waterfurnace brand thermostat downstairs and it does not change the screen to red when it is using auxiliary heat. It simply says auxiliary heat on the display. Also, I have noticed that with auxiliary heat, I seem to get a varying amount of wattage being used by the compressor while the auxiliary heat is going.

I am still getting used to all the data from the symphony system and trying to learn more about how all this works. Thanks for all your replies and information. You guys are very helpful.

 

Your loop configuration and soil looks similar to mine, except here in the Richmond, VA area my installer uses three loops (six pipes) in each trench. I have no reason to think your loops are undersized. If your entering water temperatures stay above 30 at the end of the winter you should be fine.

For comparison, my climate is very similar to SC and I have a single 4T unit for a 2,900SF house with three levels. My house was built in 1989, so my insulation might be better.

I would expect your downstairs to need more heat than the upstairs. Downstairs has 50% more square footage and hot air rises, so some of the heat from downstairs will migrate upstairs. Six tons may be enough for the house overall, but you probably need more than half of that downstairs in winter. My single system is zoned, and I need to set the zoning to allocate 75% of the capacity to the downstairs in winter to get even heating. In summer I need to set it to 50%/50% as the upstairs needs more capacity then.

If your installer did a detailed manual J load calculation you could check to see what the relative loads are for upstairs vs downstairs in summer vs winter. But, from what you've written it sounds like you may need more than 3T for the downstairs space in winter, or there are problems delivering heat to the space, such as inadequate airflow, air leaks, or needing to insulate the ducts.

 

Sshaw,
Thanks for your input. I am very interested in learning about your zoning and how that was set up.

How wide were your trenches? Mine were 3' wide. I'm curious about how much space a loop needs in order to get the best performance from the soil surrounding it.

I believe we definitely need a larger unit for the downstairs. We may need to have the ducts addressed. The first registers in the line blow like a blast furnace while the last couple rooms are frigid. But all the ducts are new and are insulated R-8. It could be that the unit being on one far end of the house doesn't allow for an optimal dispersal of the heated air. It was placed there because that part of the house has the tallest crawlspace. The old gas package unit was more centrally located and seemed to disperse the heat a little more evenly even though it was a much more shoddy job than what the new guys have done.

In general, what percentage of the time do most units run on auxiliary heat? I have spoken with one gentleman here who has a new, well insulated house that didn't even put heat strips in his unit.

In the end, I trust our contractor will take care of our problems. His company has a good reputation and I spoke with five different people who have used him in the past and everyone said good things about him. However, I feel like I should get as educated as possible so I can contribute to solving the issues.

 

Hopefully the new ductwork has a damper on each hose running to a register. Sounds like a bit of duct balancing is needed. Reducing the air flow of some of the first registers on the supply run until temp differences in rooms is closer.

Some rigid foam board over the 6” fiberglass air sealed to framing would help with some first floor heat loss.

Aux heat usually is set up to come on when heat pump can’t keep up. If temp drops 2 degrees below set point aux will come on to assist heat pump, not shut it off like emergency setting would.

When I hear outdoor reset I think it may be a southern climate thing or air source heat pump mindset.

Chris

 

My zoning uses the Waterfurnace Intellizone2 system with a 7 Series. It might have been possible for you to use zoning with a single heat pump, if your ducts could have been routed to a single heat pump. In theory you could use zoning to send some of your second floor capacity to the first floor. Separate systems for separate floors has its advantages too though.

My trenches are 3' wide. See photo below. The idea is you can put more loops in one trench to reduce the overall trench length required at the expense of extra pipe. Six pipes is normally the limit, with a slinky being the next and final step in the concept. Your loop spacing is fine.

It's common to design a system so AUX is not needed at all. However, it's also valid to design a system so AUX is needed for a few hours a year on the coldest days. What isn't valid is for the AUX to be required so much that the heating costs exceed that of a less expensive heating system, like a furnace or ASHP. My system is designed to not need AUX, but it was coming on this January when temps were below the design temp and I had forgotten to close my fireplace damper. That shows the impact of air leaks, I suppose.

 

Here are the numbers from the systems for this morning as provided from Symphony:

Outside temperature this morning: 30° with 4mph wind

Upstairs unit set temp: 70°
System is reaching the set temp. In stage 1
Loop temp: 51.3
Supply temp: 95.5
Return temp: 69.6
Compressor: 1178 watts
Fan: 112 watts
Loop pump: 246

Downstairs running in Stage 2. Thermo set for 71° but system is not satisfying the thermostat. Current temp in room with thermostat: 67°
Loop temp: 40.9°
Supply air temp: 90.7
Return temp: 67.3
Compressor: 1786 watts
Fan: 259 watts
Loop pump: 236°

That's all the info I have from the symphony platform. I don't see anything glaring... except that the system can't satisfy the thermostat.

 

we don't have a loop flow in the data but loop temps are plenty warm enough to produce heat so downstairs unit is just too small to keep up - probably needs to be 4ton unit. But your data indicates the heat pumps are on their own individual loops and not one combined loop? is that correct (which would be unfortunate)? Also the wattage being used by the fans and loop pumps seem very high. I thought the 5 series has variable speed fan so the wattage for the fan suggests restrictive duct work (ie ducts too small).

The loop pumps are probably single speed grundfos units? wattage being used makes it seem like they are the up26-116 units and not the favored ups26-99 units (116 units use more electricity for not much additional flow. Typically, if 116 pumps work, then 99 are fine. Not sure we have enough data to deduce all that though with the two separate loop systems.) see attached loop pump curves to see what I am talking about. upstairs in stage 1 using 246 watts suggests it is flowing about 8gpm in the loop which is okay but would be slightly low for 2 stage operation of the heat pump. But downstairs in stage 2 using 236 watts suggests it is flowing about 6gpm which would be too little for the 3 ton unit especially in stage 2. That might be part of the issue with the downstairs unit not producing enough heat - it doesn't have enough flow due to restrictive plumbing. Need to know more about the loop plumbing - are these on the same loop or seperate loops? so might be several issues conspiring here.

 

The two units were definitely set up with their own individual loops. Each unit has two trenches with two loops in the trenches.
My contractor mentioned to me that the unit was pumping 11 gpm. So far as I know, all we specified to Waterfurnace was having the intellistart feature, and the specific type of heat exchanger coils due to the water conditions. (We tested our water quality and made sure we met their specs). Doesn't Waterfurance determine the type of pumps in their units? I didn't know there was choice to be made. According to waterfurnace, the units have variable speed ecm blower motors.

 

link to your WF units' performance data: https://www.waterfurnace.com/literature/5series/sc2500an.pdf your units performance are on pages 62 and 63. 3ton unit running in first stage data is on page 62; second stage data is on 63.

Waterfurance typically uses a customized flow center from Geo-Flo for residential units that is just a rebranded Geo-flo product that can be found here: https://www.geo-flo.com/flow-centers/double-o-ring-oem-modules/
From that link you can see that they use a combination of 1 or 2 Grundfos pumps in each flow center. Can you confirm this is what you flow centers look like and the pump model installed? (although your energy use data suggests that each flow center has a UP26-116 grundfos pump installed)? I've attached the performance data for the grundfos pumps (power data attached in my prior message).

For the upstairs model running in stage 1 with incoming water temp of ~50F and an implied ground loop flow of 8gpm (based on the 246W figure and UP26-116 grundfos power curve), you can see that unit can produce 27MBtu/hr (HC/heating capacity column) using ~1.68kW for the compressor and fan (yours shows less energy use with compressor+fan =1.29KW). not sure what to make of that the difference - maybe others know. I believe the WF numbers don't include flow center power.

For the downstairs model running in stage 2 with incoming water temp of ~40F and an implied ground loop flow of 6gpm (based on the 236W figure and grundfos UP26-116 power curve), you can see that unit is somewhere between 37MBtu/hr and "operation not recommended". Power use is listed as ~2.3kW for the compressor and fan (yours shows less at 2.05kW). So what I was indicating above in reply 16 is that it is possible the downstairs 3T unit is generally undersized for the heating load but it also seems to be teetering on the broadline of not enough loop flow and the reduced loop flow might be limiting the unit output making it seem like the unit is undersized. Its hard to know without a manual J heat load calc to compare with but certainly the loop flow for the downstairs unit needs to be higher (assuming you confirm I have the correct flow center/loop pump config).

Since the UP26-116 is a single speed pump, you can use the performance data to infer the head loss in the loop. In the attached performance data, it indicates a head loss of 32ft for the upstairs system (at 8gpm flow) and a head loss of ~33ft for the downstairs system (at 6gpm flow). You posted above about each ground loop having four runs of 0.75" pipe but the header is a 1.25". How long are the 1.25" header pipes from the units to the 4 pipe split header location? Since the 1.25" header pipes see the full flow of each unit (before the flow gets split between the 4 individual loops) that portion of the pipes can create large head loss if there is a long distance. 0.75" loop pipes are common in horizontal systems but the header needs to get sized to minimize head loss or you get reduced flow. And the units need a minimum flow to operate as you can see in the data. 3gpm/ton is the typically recommendation for a closed loop system.

 

I will have to take the service panels off and find out what is inside there. I'll get back with that info. Thanks again.

 

look at that link I posted for geo flo products for what your flow center should look like. your flow center should be a separate black boxish type piece of equipment (with ground loops pipes going to it/coming from it) not inside of the WF unit (so don't need to remove service panels) - it might be attached to the outside of the WF unit or separately on a wall or nearby the WF unit. Some geo manufacturers include a flow center built into the heat pump but I'm not aware of WF doing that (unless something has changed/you have a unique unit). pump model should be listed on the surface of the Grundfos unit. FYI, if you have low flow in the ground loop, you could very well have cooling problems mid-summer too for the same low flow condition affecting heating. Geo units need a minimum flow in the ground loop just to function. Your downstairs unit flow seems borderline non-functional which may be presenting as a unit that is too small for the heating load when in fact the unit can't get enough flow to function properly.