Dual-fuel HVAC vs geothermal heat pump

[strawmyers]

Long story short, HVAC guy says the furnace is toasted beyond what's financially worth trying to fix. Also, AC unit is undersized for the house (PO added 1000ft^2); so I had intended to replace it this summer anyway. Original plans were this:

Bryant Plus 90i furnace
Byrant Preferred series 4 ton HP
Evolution controller

I'll try to portray the following situation without naming prices per forum rules; so bear with me...

So I asked the guy about a closed-loop geothermal HP, and if it was a viable option. He guestimated a geothermal system similar in performance to the above dual-fuel set-up would be roughly double the cost. But...

Considering the 30% tax credit with no cap on the geo HP; it shaves the overall difference in 1/2. What I'm spending in propane right now, the rest of the gap will be bridged in less than 2 heating seasons of not buying propane.

People talk about how expensive a geo HP system is and how its really only worth it for a new construction or if you're going to spend decades in the home... so what am I missing?

What features do you consider essential for a geo HP system? Any specific brands/units you'd recommend that would have similar performance and controllability to the above dual-fuel system?

[hvacvegas]

Long story short, HVAC guy says the furnace is toasted beyond what's financially worth trying to fix. Also, AC unit is undersized for the house (PO added 1000ft^2); so I had intended to replace it this summer anyway. Original plans were this:

Bryant Plus 90i furnace
Byrant Preferred series 4 ton HP
Evolution controller

I'll try to portray the following situation without naming prices per forum rules; so bear with me...

So I asked the guy about a closed-loop geothermal HP, and if it was a viable option. He guestimated a geothermal system similar in performance to the above dual-fuel set-up would be roughly double the cost. But...

Considering the 30% tax credit with no cap on the geo HP; it shaves the overall difference in 1/2. What I'm spending in propane right now, the rest of the gap will be bridged in less than 2 heating seasons of not buying propane.

People talk about how expensive a geo HP system is and how its really only worth it for a new construction or if you're going to spend decades in the home... so what am I missing?

What features do you consider essential for a geo HP system? Any specific brands/units you'd recommend that would have similar performance and controllability to the above dual-fuel system?

If you an afford it, go Geo.
Only because your on propane.
I wouldn't go Geo unless my only options were propane and oil. (personal opinion)

Decades isn't a true statement on the return on investment. Especially with the cost of propane. Decade, I can believe, but thats not factoring the price of the alternative into the mix.

In my area, electric strip heat with heat pump is considerably more efficient than propane.

If you were on natural gas, I'd say go duel fuel.

If you do go duel fuel, maybe the cash you saved and go tri-fuel. Propane/HP, and throw a wood burner in ;).

[chuckcrj]

Go with Geo. Way better choice than LP. Our electric rates are .115 per KWH and we are seeing 6 to 9 year payback with geo over propane. Good investment.

[motoguy128]

If you're on propane and have plenty of land for geo and can afford it.. go geo. Make sure they put in enough loops. Better to have more than you need, especially since soil can take some time to settle and achienve full heat transfer. Get a good load calculation done. You defnitely don't twant to be oversized... sicne it increases you installation costs significantly.

My only concern is long term. With air sourced inverter equipment closing the gap on efficiency, 15 years from now, when you're ready to upgrade, will geothermal still be the most cost effective?

[grasshopper]

Around here alot go geo with lp furnace to get duel fuel offpeak electric rates reduced about 45% of the regular rate. Between the tax credits, energy rebates and energy savings..... we are seeing way less the a decade for return.... depending on the home.

[beenthere]

Did his price guess include the wells.

[strawmyers]

He didn't specifically mention wells (didn't realize they were needed with a closed-loop system); but his statement was: "By the time you're all done, you'd probably be looking at around$xxxxx." ... so I assume that was inclusive. I do know that included the loop system as he did say that.

What is a minimum linear feet of loop for a 2400-2800 ft^2 house? There's about 1/2 an acre beside the house that could be utilized. The rest of the yard either has the septic finger system or is wooded.

What options do you guys like in a geo HP?

[hvacvegas]

He didn't specifically mention wells (didn't realize they were needed with a closed-loop system); but his statement was: "By the time you're all done, you'd probably be looking at around$xxxxx." ... so I assume that was inclusive. I do know that included the loop system as he did say that.

What is a minimum linear feet of loop for a 2400-2800 ft^2 house? There's about 1/2 an acre beside the house that could be utilized. The rest of the yard either has the septic finger system or is wooded.

What options do you guys like in a geo HP?

Theres alot of variables that determines loop length. one of which is your soil content.

Here, we see alot of 250-275' deep vertical holes, 1 hole per ton.

[tigerdunes]

Strawmyers

Before I purchased and installed a Geo HP system, I would look at and price Carrier's new high eff GreenSpeed HP system.

Then weigh your costs, tax credits, efficiency and payback between the two systems.

IMO

[Stamas]

If you go Geo consider adding a non-pressurized flow center to the budget.

[SkyHeating]

Geo all the way, where are you located? I don't think I saw it in your post, some places do wells at 200-250 ft per ton and others(like where I am) do horizontal loops at 600+ feet of linear pipe per ton. I just did a propane to geothermal conversion, check my youtube channel for Mark L Propane to Geothermal video, it will give you a good idea of what you are looking at if your are going with a horizontal loop. It is a 5 ton system, depending on your area and house you may need a 3 to 5 ton system. Mark was spending about $4,500 a year on propane in a mild year, this year has been fairly harsh and bills are estimated at $1,200 yearly.

As for features, go two stage with a variable speed blower, make sure they add a DHW(desuperheater) feature if possible. Make sure the installer has done this work before and is IGSHPA certified. Brands to look for are WaterFurnace, Hydron module/geocomfort and Comfortmaker. As you have probably read, installation is HUGE, I honestly wouldn't care what equipment was in my house so long as it was done with a proper loop and startup.

[strawmyers]

I live in central Indiana. The video was very helpful; especially the part showing the "race track" trench. When I read 600 linear ft/ton, I thought there's no way they're going to make a loop that large in the open part of my yard because I had assumed the tubes needed a few feet of space between one another. The current furnace is 5 ton. If its a 1:1 transfer between what is needed for a geo HP versus a standard furnace, that's 3000 linear feet. I think that will be viable with a "race track" in my yard. Thanks for the input!

[SkyHeating]

I live in central Indiana. The video was very helpful; especially the part showing the "race track" trench. When I read 600 linear ft/ton, I thought there's no way they're going to make a loop that large in the open part of my yard because I had assumed the tubes needed a few feet of space between one another. The current furnace is 5 ton. If its a 1:1 transfer between what is needed for a geo HP versus a standard furnace, that's 3000 linear feet. I think that will be viable with a "race track" in my yard. Thanks for the input!

The loop is not a 1:1 it is dependant on the Manual J calculation for your house. A 5 ton furnace means 5 tons of airflow it is probably a 120K BTU furnace while a 5 ton geothermal system will be between 52 and 64K BTU's of heat. A loop is sized based on size of geothermal unit, deep earth temperatures, ground lag time and heat loss/gain of home.

Just for comparison, in Indianapolis IN with a 55K BTU heat loss I am showing a 4 pipe racetrack length of 935 ft per line for a total of 4000' give or take, if you were to do a 6 pipe racetrack I am showing 710 ft per line for a total of about 4300', this assumes a silt/clay soil. This trench sizing could still vary greatly from what I put into my software since I have no idea what Indiana weather is like and if you use wells or horizontal.

[jpsmith1cm]

freonjohn,

This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.

You can find the rules for posting and qualifications here (http://hvac-talk.com/vbb/showthread.php?t=957002).

Further infractions may result in loss of posting privileges.

[strawmyers]

A 5 ton furnace means 5 tons of airflow it is probably a 120K BTU furnace while a 5 ton geothermal system will be between 52 and 64K BTU's of heat.

Stupid question... so are you saying a house with a 5 ton furnace (and 120K BTU heat exchanger) would require a 10 ton geo HP to produce the same amount of heat? 60K BTU (geo) x 2 = 120K BTU (furnace). Sorry, I have no experience whatsoever with geo stuff.

[strawmyers]

Stupid question... so are you saying a house with a 5 ton furnace (and 120K BTU heat exchanger) would require a 10 ton geo HP to produce the same amount of heat? 60K BTU (geo) x 2 = 120K BTU (furnace). Sorry, I have no experience whatsoever with geo stuff.

BTW, I'm not saying I think I need a 10 ton geo HP unit with the above statement.

[SkyHeating]

Stupid question... so are you saying a house with a 5 ton furnace (and 120K BTU heat exchanger) would require a 10 ton geo HP to produce the same amount of heat? 60K BTU (geo) x 2 = 120K BTU (furnace). Sorry, I have no experience whatsoever with geo stuff.

Short answer yes, thats a close enough comparison, however when was the last time your furnace ran for 24 hours straight? If its not running that long then your furnace is oversized, which is probably true. Your furnace is sized for airflow which is 5 tons for your 5 ton, 60K BTU air conditioner, however your heat pump will possibly be a 5 ton of airflow with 60K BTU of heating and cooling capacity. Only a Manual J load calculation can tell you how much heat your home needs during the winter and how much heat your home needs to shed during the summer. Once this is performed, your geothermal contractor will find a heat pump that will provide enough heat for you because the heat coming out of the geothermal unit drops as the temperature in the loop drops. For example at a 50 degree water temperature from the loop your unit will probably put out 64K BTU's, however in most cases the winter temperature of a loop drops to 30 degrees and you will only have 52K BTU's of heat output from the unit, thats when a backup electric heat strips or backup propane will come on to help supplment the loop. We don't want to size a heat pump for the worst case scenario because then the unit will be oversized by 20% for all but one day per year.

[strawmyers]

I think it ran all night to maintain 65* when it got down to 12* the other night (at least it was running everytime I woke up during the night); but typically only runs for less than 45 minutes at a time. The t-stat is set to 62 while I'm gone and for 70 when I'm home; and when the high was 28 last Friday it took 4.5 hours to get up to 70 with the current furnace. So you're saying a properly sized geo HP will be running the majority of the day?

I'm having a guy come out this afternoon to do a "real" load test (guy earlier in the week just made recommendations based on house size); so we'll see what he recommends. Also going to have him assess if the "free" part of the yard is adequate for an appropriately-sized loop. I guess until I know that, its not worth getting too deep into this.

[strawmyers]

Strawmyers

Before I purchased and installed a Geo HP system, I would look at and price Carrier's new high eff GreenSpeed HP system.




Could this still be paired with the Bryant Plus 90i furnace and utilize the same control unit (Evolution)? If not, what would a good pairing be with this unit?

[wahoo]

In our area (K.C. Mo.) we use 700ft./ton in an extended slinky loop dug into a trench about 125-130ft. long. As long as the soil will have some moisture. These loops don't work in dry sandy areas however. We also use the non-pressurized loop system and all our GSHP units have built in 10 to 15 KW electric back up heat. Nowadays we use only variable speed blowers with two stage compressors. You must have an accurate manual J done, and size the unit using this figure. The good part of the two stage units is that the lower speed works great on AC and the higher stage makes the unit put out more heat in winter. Make sure you get an experienced contractor and don't hesitate to ask for customer references BEFORE you hire them. These units are not the same as standard heat/cool units and experience counts!!!
If you're on propane, then the GSHP is a very good way to go!! We've been putting in GSHP since 1990, but have not ever put a GSHP onto a propane furnace. Would have to study the "why?" a lot before recommending it!

[motoguy128]

Could this still be paired with the Bryant Plus 90i furnace and utilize the same control unit (Evolution)? If not, what would a good pairing be with this unit?


The Greenspeed (and Bryant equivalent) heat pumps and AC's must be paired with the Greenspeed air handler or furnace. Its communicating equipment like hte Infinity and Evolution systems, just the next generation.

I agree, the new air source equipment is improving dramatically win efficiency. One downside in many climates to geothermal is the balance of heating and cooing demand. In my home I need 2X as much heating as cooling. So I'd need a 2 stage heat pump and still have to oversize to avoid using the heat strips.

[hvacvegas]

The Greenspeed (and Bryant equivalent) heat pumps and AC's must be paired with the Greenspeed air handler or furnace. Its communicating equipment like hte Infinity and Evolution systems, just the next generation.

I agree, the new air source equipment is improving dramatically win efficiency. One downside in many climates to geothermal is the balance of heating and cooing demand. In my home I need 2X as much heating as cooling. So I'd need a 2 stage heat pump and still have to oversize to avoid using the heat strips.

All they have to do is start using variable speed compressors, with variable speed Grundfoss pumps.

Hah. Can you guys imagine installing a unit that costs as much as a greenspeed, and a climatemaster, combined?

[platchford]

The Greenspeed (and Bryant equivalent) heat pumps and AC's must be paired with the Greenspeed air handler or furnace. Its communicating equipment like hte Infinity and Evolution systems, just the next generation.

I agree, the new air source equipment is improving dramatically win efficiency. One downside in many climates to geothermal is the balance of heating and cooing demand. In my home I need 2X as much heating as cooling. So I'd need a 2 stage heat pump and still have to oversize to avoid using the heat strips.

Isn't that a downside to heat pumps in general? At least with geothermal you have a pretty consistent output even as temperature drops. I'm not saying there is no decrease in output but it's not as bad as air source. The biggest problem with heat pumps is that just as you need more heating the output decreases... which is why I still think they work great paired with a gas furnace vs an oil or propane furnace by themselves.

[SkyHeating]

All they have to do is start using variable speed compressors, with variable speed Grundfoss pumps.

Hah. Can you guys imagine installing a unit that costs as much as a greenspeed, and a climatemaster, combined?


My WaterFurnace rep told me they have some investor compressor units with variable speed pumps in testing that are hitting 6 to 7 COP and price... Not that much more. If you know WF pricing it's expected to cost as much as a Synergy 3d system instead of a two stage envision.

[strawmyers]

Got further clarification from today. The quoted price DOES include trenching or wells (2 wells per ton at 200' each). Doing wells is ~10% more than the loop; but appeals to me more. They can fit all 8 wells in a 15'x6' spot in the yard. I'm planning to eventually add a pool and a pole barn. With only about 1/2 acre of good (non-ravine, non-wooded) part of the yard not taken up by either the septic or driveway/walkway, its nice to lose as little as possible.

Manual J came out to ~36000 cooling, ~75000 heating. On those numbers, my current 3 ton AC should be adequate; but its not. House couldn't get below 86* during the hottest weeks of the summer with AC running constantly. I realize you don't want to size a unit to the worst day of the year; but sweating in an 86* living room while the AC runs non-stop for 3-5 weeks a year doesn't work for me. They are recommending a 4 ton geo HP w/ 2 stages. Supposed to get an actual quote with model #'s early next week.

The guy didn't think a holding tank was necessary. Would that help with the output loss during cold months? My neighbor down the road has ~400ft^2 less and he has two 50 gallon holding tanks in his GSHP system. He did recommend a desuperheater. Did NOT recommend going with the cost/complexity of dual-fuel geo/LP furnace. The geo has heat strips.

What are the benefits of the non-pressurized system? He said they've done them before; but usually just do a normal pump set-up with the expansion tank or whatever its called to control pressure spikes. Said the only difference is that the return water dumps into a tank and is then pumped out versus the whole system being pressurized. He said the cost is basically the same; so we may not be talking about the same thing.

At this point, I'm heavily leaning toward the GSHP system. It will be nice to completely get away from LP for heating... and with the added good "green" karma, if I tag a squirrel or two when I'm driving, I don't have to feel bad about it.:grin2:

[strawmyers]

Got further clarification from today. The quoted price DOES include trenching or wells (2 wells per ton at 200' each). Doing wells is ~10% more than the loop; but appeals to me more. They can fit all 8 wells in a 15'x6' spot in the yard. I'm planning to eventually add a pool and a pole barn. With only about 1/2 acre of good (non-ravine, non-wooded) part of the yard not taken up by either the septic or driveway/walkway, its nice to lose as little as possible.

Manual J came out to ~36000 cooling, ~75000 heating. On those numbers, my current 3 ton AC should be adequate; but its not. House couldn't get below 86* during the hottest weeks of the summer with AC running constantly. I realize you don't want to size a unit to the worst day of the year; but sweating in an 86* living room while the AC runs non-stop for 3-5 weeks a year doesn't work for me. They are recommending a 4 ton geo HP w/ 2 stages. Supposed to get an actual quote with model #'s early next week.

The guy didn't think a holding tank was necessary. Would that help with the output loss during cold months? My neighbor down the road has ~400ft^2 less and he has two 50 gallon holding tanks in his GSHP system. He did recommend a desuperheater. Did NOT recommend going with the cost/complexity of dual-fuel geo/LP furnace. The geo has heat strips.

What are the benefits of the non-pressurized system? He said they've done them before; but usually just do a normal pump set-up with the expansion tank or whatever its called to control pressure spikes. Said the only difference is that the return water dumps into a tank and is then pumped out versus the whole system being pressurized. He said the cost is basically the same; so we may not be talking about the same thing.

At this point, I'm heavily leaning toward the GSHP system. It will be nice to completely get away from LP for heating... and with the added good "green" karma, if I tag a squirrel or two when I'm driving, I don't have to feel bad about it.:grin2:

Thoughts on the above?

[strawmyers]

Before I purchased and installed a Geo HP system, I would look at and price Carrier's new high eff GreenSpeed HP system.

Then weigh your costs, tax credits, efficiency and payback between the two systems.

IMO


Been reading up on this. Looks like the unit would be self-sustained, even in temps below freezing; and therefore would not need dual fuel (back-up furnace). Is that correct? Any benefit to dual-fuel with the GreenSpeed if the accessory heat is propane?

[hvacvegas]

Got further clarification from today. The quoted price DOES include trenching or wells (2 wells per ton at 200' each). Doing wells is ~10% more than the loop; but appeals to me more. They can fit all 8 wells in a 15'x6' spot in the yard. I'm planning to eventually add a pool and a pole barn. With only about 1/2 acre of good (non-ravine, non-wooded) part of the yard not taken up by either the septic or driveway/walkway, its nice to lose as little as possible.
Alot of times, loop temps drop pretty low with a trench (meaning low heating), since their closer to the ground. Where as vertical is less harmed(although not immune) to low outdoor temps.

Manual J came out to ~36000 cooling, ~75000 heating. On those numbers, my current 3 ton AC should be adequate; but its not. House couldn't get below 86* during the hottest weeks of the summer with AC running constantly. I realize you don't want to size a unit to the worst day of the year; but sweating in an 86* living room while the AC runs non-stop for 3-5 weeks a year doesn't work for me. They are recommending a 4 ton geo HP w/ 2 stages. Supposed to get an actual quote with model #'s early next week.
I know one thing. The last thing I would want is a undersized Geo.

The guy didn't think a holding tank was necessary. Would that help with the output loss during cold months? My neighbor down the road has ~400ft^2 less and he has two 50 gallon holding tanks in his GSHP system. He did recommend a desuperheater. Did NOT recommend going with the cost/complexity of dual-fuel geo/LP furnace. The geo has heat strips.
Diffenetly go with the desuperheater. Don't expect it to cover all the heating of water though. If you has a gas water heater, then you need to add an electric tank as a "buffer" tank. Make sure your contractor includes this. To long to explain, but you can't use desuperheater on a standalone gas waterheater.
Also, I don't know about your neck of the woods. Here in cincy, it's actually more cost effective to use electric strips/heat pump, than is it propane/heatpump, due to the high cost of propane.
Climatemaster has a great program called "geo-designer". It shows a break down of cost estimates, with side by side comparison. Get your contractor to get you a sheet with actual numbers.



At this point, I'm heavily leaning toward the GSHP system. It will be nice to completely get away from LP for heating... and with the added good "green" karma, if I tag a squirrel or two when I'm driving, I don't have to feel bad about it.:grin2:

I doubt anyone you've talk to has brought this up, but I have ran into this multiple times:
Is your electric big enough to handle the strips?
Last Geo I did required the electric company to run new wires from the pole to the house, with a ground transformer, and sparky had to setup a new panel, blah blah blah.

Make sure someone has checked your power supply. If not, it's a big unseen expense. Big, as is 15-30% on top of the cost.

[strawmyers]

I have a 200A service. I don't know what is required; but the guy did look at my panel and didn't comment on needing anything upgraded. I'll be sure to clarify with him, though. Thanks for the heads up.

The geo/propane combo wasn't about cost savings as much as having heat in th event of a multi-day power outage. Not common around here; but it has happened. I have a 7kW generator. I could run a propane furnace off of that if need be. No way that's going to run those heat strips. I'm hoping whatever the back-up heat is (propane or heat strips), that it won't hardly ever be used except during a power outage. If the GSHP isn't able to handle heating my home in the cold of winter, the large price tag makes less sense to me.

[second opinion]

I have a 200A service. I don't know what is required; but the guy did look at my panel and didn't comment on needing anything upgraded. I'll be sure to clarify with him, though. Thanks for the heads up.

The geo/propane combo wasn't about cost savings as much as having heat in th event of a multi-day power outage. Not common around here; but it has happened. I have a 7kW generator. I could run a propane furnace off of that if need be. No way that's going to run those heat strips. I'm hoping whatever the back-up heat is (propane or heat strips), that it won't hardly ever be used except during a power outage. If the GSHP isn't able to handle heating my home in the cold of winter, the large price tag makes less sense to me.

If you want to hedge your bet on the power outage the propane with your generator would be the way to go unless you upgrade to a 30 kw generator.

If installed properly and all parameters are covered in the design of the geo system it will handle the cold or heat.

making sure that you thoroughly check out your installer/designer and any subcontractors that they may use.
I have seen a lot of geo failures due to lack of knowledge on the contractors part. There is a large dollar cost up front and any mistakes can prove costly to remedy.

[wahoo]

The two large advantages of the non-pressuized system with built in reservoir is:
1. The homeowner can actually check level of loop solution while unit is running and add anti-freeze solution if needed. The first few months of operation "adding" is not un-common, but still should be checked once or twice a year.
2. The outside loop (and pumps) are subjected to less pressure. In a "closed" system you must maintain positive pressure (we use @20-30 psi) but in open system this actual loop pressure while running is about @8psi and nothing when idle.

Oh yeah, another thing is the elimination of the darn "peats plug" pressure checking fittings which tend to leak after a few years and lose the pressure in a closed system!:.02:

[strawmyers]

I can tell I'm going to have to take a stand for the NP system if I want it. The previous guy said it really wasn't of any benefit; and the guy this past week basically said its just something someone came up with to help mask some of the issues of a poorly done install. He said they pressure test the loop system at 150psi; which also pre-stretches the tubes, eliminating the need to add more fluid later. Also stated they heat fuse all elbows/fittings onto the line; so there's no chance for leaks. He did also say it would be more expensive with virtually no return benfit; but I got the feeling that statement was made mostly because he thought the phrase "more expensive" would deter me from persuing the issue any further. The last guy did seem a lot more knowledgeable about GSHP. Made me feel more confident about their company possibly being the one to do the install. Mostly a nice, friendly guy; but there were a few times he was bordering on cocky and didn't seem as receptive to customer input (NP system being an example) so that didn't sit with me quite as well.

[edit] BTW, its going to be a split system due to space constraints, with a new propane furnace as emergency/auxillary heat instead of heat strips. I don't know if any of that would matter in regards to the pressurized vs NP set-up.

Versus opening a new thread, I'll ask here. Can anyone sell stuff in the 'junk yard' forum, or just pros? I'm hoping to sell some of the "good" parts of my current system to help recover some of the GSHP costs.