Integrating Geothermal with and oil fired boiler backup

Keith McKinley

gary,
which course did you take? I'm looking at their web site and thinking of taking one.

It is a lot of water and their is no reason the HP cant keep 125 degrees in the buffer tank, My AH has a 41K BTU rating at 140 degrees water temp so I won't have an issue running at a lower temp to provide the 18K BTU's I need.

As for the Juice to move the water. I agree if it's a standard well pump setup which will short cycle. But a variable speed pump will not short cycle so that should be a bonus, plus I have a shallow well. Still not as good as a 1/6 HP recirc pump on a closed loop system, but, I can buy a lot of pump "juice" for the 20K the local geo guy wants to drill and install three 300 ft vertical loops.

Keith

Keith McKinley

Integrating Geothermal with and oil fired boiler backup

Sounds fairly simple but..........

Currently have an oil fired boiler suppling hydronic heating through 3 air handlers each on it own zone. Each zone has a Taco pump mounted on the return side of the system. My total heat loss is 62,000 btu

I would like to install an open loop geothermal system rated at 60,000 btu with a desuperheater for DWH. I've already established that the Geo unit will be coupled to an 80 gallon buffer tank which will provide the load to the house.

I would like to keep the boiler in the system as a back up and tie it to the buffer tank as well. If by chance the buffer tank can't keep up with the heat the lower temp thermistor in the tank will call for a heating element to augment. Instead of that heating element being called. I'd like my boiler to be called. Seems logical to me but am I missing something?

Now, what would be the optimum method be to tie the two systems together? I suspect I need a recirc pump from the boiler to the buffer tank. There is already a built in pump from the Geothermal unit to the buffer tank. Also, Should I remove the three recirc pumps currently in the system and replace them with zone valves and a single recirc pump from the buffer tank.
I'm also thinking a 3 way zone valve might be the best option to tie in the oil burner?

In my mind all the systems are isolated to some degree yet working together.

for sure the geothermal and oil boiler are isolated from the heating loads by the buffer tank.

Thanks in advance for your expertise!

Keith

ScottMP

Great Question Kieth

I thought you where my customer for a minute

I hae a job I am bidding with the same set-up ( New England ) and would love to hear the answers and thoughts on this.

Scott

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Keith McKinley

I'm in MA

contact me at keith@mckinley.us

As I get some feedback I'll keep you posted. I've got other feelers out as well. In any case this seems to be more common sense than anything.

K

jack_40

Very simple

I have done 9 or ten systems like that. The best way I have found is a two stage aquastat or useing two aquastats set 15 deg apart. and inject into buffer tank from boiler very simple and works great plus all components are avalable at any supply house. Just connect the second aquastat to the argo on the boiler and your done. Simple two stage heat.

The only problem with this is that with the low temps of geo the boiler will never hit 180 but with the heating load you have i think the boiler will only fire for domestic water from time to time. You probably will never need the backup if the system is sized correctly.

Why are you going with a 80 buffer tank I would use a 40 the only reason that the buffer tank is there is to prevent short cycling. With 80 gallons that may be to much and use more energy. why store 80 gallons when you probably only need 40 or maybe 50.

Mike A

Keith McKinley

Thanks Mike

Are you in the New England area by any chance!

A couple things about your comments:

Shouldn't I just turn down the boiler so I don't need a top end of 180?

What is the argo?

What is the best way to actual plumb the oil boiler line into the geo - buffer tank loop. I'm guessing just T-ing in on the supply and return side with check valves. No fancy mix valves needed?

As for buffer tanks. I know the rule of thumb is 10 gallons per ton but I was looking at a Water Furnace buffer tank and the smallest was 80 gallons. Plus I'm running 16K btus of radiant heat in the system as well.

Most importantly, what company do you recommend for a water - water geothermal system operating on a well open loop? I'm looking at the big 3 climate master, water furnace and econair.

As for DHW I'm getting the desuperheater option so that will take care of that except in the summer when I'll use the oil (with a separate injector or just gp straight electric) Oh ya I'm using a heat only geo system

Thanks!

Keith

Keith McKinley

correction Mike

I know what you mean regarding the aquastats, temps and the argo.

Let me add one more question to the bunch regarding the boiler splice.

I plan on running the buffer tank at 125 degrees with a 105 degree call for heat. Now if my system was undersized or maybe sized right on the money with extremely cold temps it seems that the heat pump would just continually run to try and get the 125 degrees in the buffer tank.

Would I cause any problems to the heat pump system injecting that 140 -180 degree boiler water into the supply loop to the buffer.

Do you know of a good schematic showing this set up

Wayco Wayne_2

I'm looking at the same thing

on a job where the heat pump was undersized for the heating load, and must be supplemented by a gas boiler. Tekmar tn4 has a two stage control with an adjustable time delay so the back up boiler won't come on unnecessarily. The system will also maintain the outside reset curve while doing it. Wow!

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Keith McKinley

what were the numbers?

heat loss in btu for the home and the size and brand of the geo thermal unit? I noticed climate master shows a gsw 060 model leading you to believe it puts out 5 tons. The HC is just at 4 tons at all flow rates

Keith

A.J.

alittle off topic

Sorry to barge in guys but I had a question that I just can't seem to get an answer to from the equipment manufacture. We are in a heating dominate area so are cooling loads are typically about half the heating.In a typical forced air system how do you size for the heating so you do not use alot of strip heat without extreamlly short cycling the geo.in the cooling and lossing the the ability to dehumidfy. I looked at dual capacity units but the defference between stages is not that big and we are still oversized on first stage cooling. That are guys doing if anything to get around this?

Craig R Bergman

Rule of thumb

A minimum of 10 gallons of buffer per ton is required.

Bergy

Craig R Bergman

Why heat only units??

Why not allow the Geo to provide chilled water for the hydronic coils? It would be a shame for you to do all the work of plumbing in Geo and not take full advantage of it's
capabilities.

Our shop has never done a boiler back-up so I can't help with that. The attached JPEG shows how we pipe a heating and cooling Geo into a Radiant and Air Handler system.

Bergy

Bob Bona_4

Craig

Have you any experience w/ DX?

I'm starting the mechanicals for a home that will have three seperate "air handlers" next week. The house used to have one oil fired furnasty for the first floor, and a heat pump for the second. Electric HW. They are adding a studio that will need two ton of cooling, and I have already roughed in slab hydronic radiant and underground ductwork.

Sundial from Hartford CT is doing the well and the trench to the house. I take over from there.

Craig R Bergman

Bob

We do not have experience with DX systems. All of our closed loop systems are HDPE pipes.

Bergy

GW

yes

It seems like everyone interested in geo hasn't been to geo 101. I'm still a novice myself. I learned a lot of stuff at the IGSHPA training I did a few seeks ago. I have a 3 ton WF Envision at our place of business.

I'm wondering how the 5 ton geo water to water is gonna work for this situation; and with open loops, wow that's a lot of water, lots of juice to move that water.

When it gets real cold out I'm guessing you're gonna run just oil and drop out the HP. Afetr all, unless your AHUs can heat the home with 100deg air, you've got issues.

No AC? That's odd.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Craig R Bergman

Size the Geothermal unit

to handle 92- 97% of the heat load. Size the Aux electric as you wish. We normally use 10K strip heaters. A 20K unit was once used per the HO request. If the Geo has a Twin Single your split will be 60/40. If it has an Unloading Scrool the split is 70/30. Remember, the air coil is on the low pressure return so moisture condenses very well.
We have had no problems with too much cooling, yet. If you do, Dehumidification is part of the controls on the better units.

This is one of the reasons a Geo system CAN NOT be installed by a "rule of thumb". Close attention MUST be paid to both Heat Loss and Heat Gain for the structure.

Geothermal Heat Pump manufacturers have been playing a little "slight of hand" in sizing their equipment. They are putting in smaller compressors to make the COP and EER numbers look better!!! Look closely at the heat of extraction and the heat of rejection numbers for the Geothermal unit. DO NOT assume a five ton unit will give you 60,000 Btu/hr with 30* entering water temp.

Bergy

A.J.

Thanks Craig

Your right about the output on the units a four ton was the output of a three and a five has the output of a four.
The one we are looking at has an unloading scroll the split is about 80/20. I will check on the dehumidifcation feature.