I have decided to convert my late 1950's ranch 2100 sq ft in the Philadelphia area with an oil based boiler (hot water baseboards) to Geothermal. Can anyone provide direction as to system size? I have received 4 quotes- 1- 3ton, 2- 4 ton and a 5 ton system! Also, there appears to be a difference in basing the system on cooling vs heating.... Thank you!

Ask who has performed a manual J calculation to arrive at recommended tonnage.

Geo is pricey per ton - consider ways to reduce house load - infiltration reductions and insulation upgrades to reduce load may prove cheaper both upfront and in the long run than adding an extra ton of geo.

Size for cooling, or at least don't oversize for cooling more than a fraction of a ton, then make up the difference with electric strips.

I think you mean heating........

I do mean cooling.

Posted By engineer on 14 Mar 2012 09:59 PM
Ask who has performed a manual J calculation to arrive at recommended tonnage.

Geo is pricey per ton - consider ways to reduce house load - infiltration reductions and insulation upgrades to reduce load may prove cheaper both upfront and in the long run than adding an extra ton of geo.

Size for cooling, or at least don't oversize for cooling more than a fraction of a ton, then make up the difference with electric strips.

Curt, while Philly is a bit more balanced, for example our cooling load is about 50% of the heating load. If we would size for cooling, our systems would be way undersized for heating, and our customers would be very unhappy. Run time is 90% heating and 10% cooling. This is where 2 stage systems do wonders, since they limit the over sizing compromise we have to do for cooling.

Thank you for the replies! If we size for cooling won't we be using auxiliary (electric) for a portion of our heating and increase operating costs? Is there a formula to figure out our annual temperature range here? Can operating costs be estimated? This system will be making our hot water too.

Sounds similar to my path down the geothermal expressway!

I'm in South Jersey and have gotten quotes from 6 tons to 2 tons - Some said to size for heat and some said to size for cooling.

I've learned alot from the people here - it's good to get as much information as you can on this as you want a good system in the end.

Sizing for cooling was single stage and southern climate practice. 2 stage heatpumps have helped to serve both needs better. Philly is much better than Western New York since you ehating load is less and your cooling load is more. Still can't see it working well when sized for cooling only.

Posted By BW on 15 Mar 2012 05:57 AM
Can operating costs be estimated?

Absolutely. A competent installer can predict your operating costs
within a few percent -- for everything: heating, AC, and hot water.

Don't even consider hiring an installer who doesn't provide you with
a complete -- and guaranteed -- operating cost projection.

See the thread: "Geothermal in old house in Wayne PA"

Looby

Lobby - did you size your system based on heating or cooling? Sounds like our scenarios are similar.

Sorry - meant to type "looby"

Posted By BW on 15 Mar 2012 09:10 PM
Lobby - did you size your system based on heating or cooling? Sounds like our scenarios are similar.

I didn't size it, my contractor (sintonair.com) did -- and he NAILED IT.
His op cost estimates were dead on, as were his predictions of running
hours, loop temperatures, etc. Most importantly, we're saving gobs of
cash -- while enjoying far more comfortable temperatures, year round.

My Manual J heating load was vastly greater than the cooling load, so
I'd have to say the design was based heavily (entirely?) on heating.
However, my house is on a heavily shaded lot, in a steep valley with
less-than-average sun, and cool babbling brooks on two property lines.
So, it's substantially more heating-dominated than the average Philly-
area home.

I'm a retired engineer, so I felt comfortable that my BS-detector was
good enough to distinguish between competent pros and snake oil
salesmen. Once I found the guy that seemed to know what he was
doing, I let him own the design. Of course, he also had to sign the
system performance guarantees.

good luck,

Looby

Posted By BW on 15 Mar 2012 09:39 PM

Sorry - meant to type "looby"

No wurries, I've been called much worse...

...frequently,

Lo[ob]by

sizing is not based soley on load but also cost/kwh. in mid MI we tend towards cooling load + 1 ton, but- our electricity is cheap.

Any thoughts as to the following?

One of the contractors that provided me with a quote said that a cost analysis was impossible because they didn't know factors like leaving doors open, degree the system was set to operate etc...

I hate keep asking but is there any definitive way to base sizing a system in the Philadelphia are - cooling vs. heating?

A competent installer can predict your operating costs
within a few percent -- for everything: heating, AC, and hot water.

If you read through this forum, you will find cases where professionally done Manual J's disagree with actual usage figures by > 50%. It's not at all exact.

Posted By jonr on 16 Mar 2012 08:14 AM
It's not at all exact.

Is that your [chortle, chortle] "professional" opinion?

Posted By BW on 16 Mar 2012 06:12 AM
Any thoughts as to the following?

One of the contractors that provided me with a quote said that a cost analysis was impossible because they didn't know factors like leaving doors open, degree the system was set to operate etc...

I hate keep asking but is there any definitive way to base sizing a system in the Philadelphia are - cooling vs. heating?

An answer like that would raise the BS red flag. It is true that a 1950 house is very unpredictable, new houses are easy since you know very well the R values. In older one you have to guess pretty much how the r value of each wall is. Best to get an energy audit and a blower door test. Even better to use your previous consumption. Philly should be within a ton between heating and cooling, you will likely end up between 3-4 tons. Make sure you get a dual stage HP.

BW, while I rareley get accrossed the bay to drill, my service area is simmilar to south Jearsey. Here a variety of tools are used to come up with the perfetct design. Some of the parameters are:
year round residance or only summer
rental or primary
life style

Most installers here design for 100% heating load and cooling load. Then they work the design backwards in heating to see if they can reduce tonnage by inserting a given number of degree days per year that stage 3 heat will be employed. Put all that in the blender, cross check with the budget available and presto.
Eric

Kinda funny - Kinda not so funny but this sounds similar to my experience ( i live 40 minutes from Philly ) and had a hell of a time selecting a contractor.

No BIN reports, no clear cut answers for tonnage, etc.