Geo Thermal 1 5-Ton Unit Vs. 2 2-Ton Units

H Welch

I am building a house all new construction. Due to the change in the Fed Tax Code Geo Thermal is now on the table as an option. I have recieved 4 quotes: All have prices as a single 5 ton system. However 3 of the 4 suggest ideally I go with 2 2-ton Systems. This bumps the price up significantly. I find the reasons to split the system as "suspect".

Please give me your biased or unbiased thoughts on a single or split system.

Mark Custis

Need more input

It depends, (Dan H. might put a button that types that in the works), on how the geo system(s) is sized.

Are you trying to go 100% geo without back up?

What is the heat loss on the home?

What is the usage of the home? Will large areas be idle for periods of time?

My boots are not on site, so more input.

Singh_9

hydronic or air?

It could be that the quotes for two are factoring in smaller radiant zones without a buffer tank, and that can be ok.
If one 5 ton is used and a zone comes on without a buffer tank, the HP compresser can short cycle, and that's not efficient.

H Welch

The single unit would be a 5 ton Hydroheat Megatek. This is a two stage hydro system. The unit will provide 100% heating and cooling and residential hotwater. System has a back up heat built in. I live in CT - right on Long Island Sound. I have been told any system in this local will be even more efficient due to the high water table.

House is new construction, 2X6 construction, new Jeldwen windows (low eglass), insulation 2inches of closed cell and 4 inches of fiberglass. Tight envelope is the goal. Total living space of 3200 square feet average 8 foot ceilings.

The guys pitching the split 2 2ton systems reasoning is quieter, and easier to install. I think it helps that they would book an additional 15-20K in sales

Mark Custis

I have two units in Waterford

and the customer swears I got the electric meter to run backwards. I know that there is no net metering at the location.

It costs a lot to do business in CT. I am designing two system around Salem for install this summer.

Still need more input to grasp the differance in the two ideas.

Hwelch

What additional information do you need?

Is there a preferred system build you use?

Unknown

if it's hydro, you should be able to nix most of the difference between the two approaches by sizing the buffer tank properly.

Constantin

Well, for starters...

What kind of heating and cooling emitters do you plan on using? What is the actual heat loss and gain of the structure? Are the COPs of the two systems comparable? Will the cooling portion be to two air handlers or just one? Etc.

For example, I have a conventional air-based AC system consisting of two condensers and two air handlers inside. That made sense in our house since the old lady has little to no room for ductwork and having two air handlers minimized it. However, a single 4-ton unit outside would be just as capable of cooling the house as the two units we have now.

Some day, we may see more inverter-driven compressor systems and EEV systems in this country, which would allow single outdoor units to service multiple indoor units. However, considering how stone age most HAVC control systems are, I am not holding my breath. A manufacturer would have to control so many aspects of the product that many installers might abandon it for that reason. An open-standard RS485 system could help push the industry forward since it would allow thermostat, etc. manufacturers to norm around one standard, not six proprietary ones.

Anyway, there could be some efficiency gain from splitting the compressor load among two compressors running single-stage vs. using a single a multi-cap compressor. For example, comparable capacity systems with tandem single-stage scrolls vs. a 2-cap scroll usually score higher on EER, even though COP usually rises with capacity. Another benefit of dual systems is redundancy. However, as others have stated, the devil is in the detail, i.e. how the system is set up, what kind of a buffer tank is used, etc.