Generator backup for geo-thermal?

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GerryB

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woodbridge, ct. USA
Recently I was reading an old post about tankless hot water heaters. I agreed with everyone who thought they were not that great, stupid wiring, etc. Soon I am doing a new house. They are not going with tankless hot water, but they are going with geo-thermal heating and cooling. The contractor called me the other day and said the HVAC guy told him we should do a 400 amp service because there are two units and one draws 70a on start and the other 40a. He said people complain about the lights dimming. OK, the 400 amp is no problem, the service is extra. Problem is, they want a generator, auto start. They were talking about a 20k generac, which I think is about 80 amps. The HVAC guy was talking about these loads on cooling but I am assuming they are the same for heating, so to have heat in the winter they are going to have to spend twice as much or more on a much larger generator. Comments?
 
The 70 and 40 probably include electric strip heat as an emergency back up. Have them change that to gas which would reduce your potential load dramatically.
 
I don't care what size service you install, the lights are still going to dim because of the lack of supply from the utility company...

I'm doing the same exact setup up Gerry, geo thermal, 320 amp service, 200 amp ATS for one of the 200 amp panels, we didn't size the generator yet because we don't have all the loads and what equipment is being installed yet, but I'll let you know as the job progresses, but it will be awhile... this one is slow moving.
 
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GerryB said:
Recently I was reading an old post about tankless hot water heaters. I agreed with everyone who thought they were not that great, stupid wiring, etc. Soon I am doing a new house. They are not going with tankless hot water, but they are going with geo-thermal heating and cooling. The contractor called me the other day and said the HVAC guy told him we should do a 400 amp service because there are two units and one draws 70a on start and the other 40a. He said people complain about the lights dimming. OK, the 400 amp is no problem, the service is extra. Problem is, they want a generator, auto start. They were talking about a 20k generac, which I think is about 80 amps. The HVAC guy was talking about these loads on cooling but I am assuming they are the same for heating, so to have heat in the winter they are going to have to spend twice as much or more on a much larger generator. Comments?
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Anyone that is going to pony up the money for geothermal can afford to have an engineer design the entire mechanical system. I'd ask for engineered drawings, including the generator. And, quite honestly, I wonder why the HVAC guy is sizing the service. When's the last time you told an HVAC guy what size heating system to install?
 
Speshulk said:
Anyone that is going to pony up the money for geothermal can afford to have an engineer design the entire mechanical system. I'd ask for engineered drawings, including the generator. And, quite honestly, I wonder why the HVAC guy is sizing the service. When's the last time you told an HVAC guy what size heating system to install?
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LOL, I know... thank god the HVAC guy saved the day. The job I'm doing has NO drawings, I can't wait to see this mess unfold.
 
stickboy1375 said:
LOL, I know... thank god the HVAC guy saved the day. The job I'm doing has NO drawings, I can't wait to see this mess unfold.
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Be careful with that one. You're leading with your chin. When it doesn't work, you know who the fingers are going to get pointed at.
 
just finishing up a house with the same set up, GEO, with Gen backup. However I am not supplying the GEN nor did the calculations for it.

The HVAC said he can wire the GEO furnace so only the pump and blower will run on the GEN, the ground temp is only 55 to 58 degrees but will still be warmer than the outside and keep pipes from freezing, summer time no problem cooling.

Doing this drastically lowered the size of the GEN
and only going to backup one of the two 200a panels, but only going to backup with about 100a
 
I don't understand. You said one draws 70a, the other draws 40a. You also said this is a house so I am assuming the voltage is 240. 70+40=110a x 240 is 26.4 kw, so why would they install a 20 kw generator?

I would gather the motor cut sheets together and any other loads that will be running/starting simaltaneously and send them to a generac dealer, or cummins if there is money in the job. The dealer will take into account the motor codes etc. to ensure the generator has enough skva etc. to start all the motors. The dealer will size the generator for free and then it will be their neck on the line should something go wrong.

Also, if this is geo thermal you will probably have water source heat pumps in the house. These units typically draw the same for cooling and heating because they are using the same process just with a reversing valve in the hvac unit itself BUT sometimes these units will have supplementary heat strips which you will have to take into account for heating. This means when you size the generator you will have to take into account any pumps running, the hvac unit, and the heat strips plus any additional loads in the house. Many geothermal systems have two pumps in parallel but only one will run, the other is a backup.

Good luck.
 
The reason they think they are going with a 20k is because that's the popular one you see on line when you look and don't really know what you need. There is money in the job though because to build this house they are knocking down (have knocked down) the original house which ain't to bad looking to me. I like the feedback from everyone and I was already planning on letting the generator people size the thing. Like you said Stickboy the lights are blinking anyway, this is an underground service, 50 feet to a yardbox we put in a few weeks ago for the temp, so the 350's from the house will splice to the old 1 ought?(how do you write that?) from the POCO's direct burial that goes across the street to the transformer. The POCO engineer said kind of offhandedly that he might have to up the transformer someday! I'll have to run some of these ideas also by the HVAC guy, like using gas or just wiring the pumps etc., but don't they always size the service?(post7) Seems like if the can't find 2 spots for their condensing unit they tell the HO he needs a new service;) Good for us though.
 
This must be a different type of geothermal system. A geothermal heating/cooling system doesen't typically use condensing units. Condensing units are for air cooled systems, you have a water cooled system but you are using the earth to pre heat/cool the water.
 
Npstewart said:
This must be a different type of geothermal system. A geothermal heating/cooling system doesen't typically use condensing units. Condensing units are for air cooled systems, you have a water cooled system but you are using the earth to pre heat/cool the water.
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No I was joking about how the HVAC guys go to someones house to do central air and if the panel is full they tell the HO they need a new service. (which sometimes they do)
 
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