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?

Op and load calcs identify parameters and set points. Savvy contractors add disclaimers. PCT savings is likely more accurate than dollars as load calcs do add fudge.

Sorry Joe - i guess I'm a bit of a novice here but I really don't understand your last post.... I do however look forward to any direction you can provide.

First, I suggest you find some better contractors. Any good one will do a respectable manual J. These can vary quite a bit though, but it gives you a barometer to gauge with and compare quotes. Don't let them feel like they are doing you a big favor by doing this. If they don't do it, its not the right guy.

For philly area, its a heating dominated area. As a better measure, take your last few years of winter oil consumption and perform a calculation to get your REAL heating load. I am not an expert on this, but if you searches on this site, there are some really good posts on doing exactly this. From what I read, these are really accurate and it's not terrribly hard to do. Maybe some of the experts can point you in the right direction here...

I think you will likely be in the 3 ton range based soley on your size and location. Add another 1/2 - 1 ton if your poorly sealed and underinsulated and subtract a 1/2 ton if you do some sealing and insulating. Your best money is spent doing some insulation work if you have not done so already. Get the 2 stage unit to get longer summer run times and excellent dehumidification. It's worth it. Have the ducting sized to give good distrubution at the lower 1st stage fan speed, but big enough for low noise at 2nd stage. Get returns from the far end of house if you can.

I live in the philly burbs, 2 story 3000 SQFT house, 4 ton 2 stage geo, solar PV, just about net zero house. I did some sealing and insulation. I now wish I got a 3 ton unit as my unit barely bumps to second stage on the coldest days and we keep it a comfy (for us) 68 F. My friend also just had his ranch house attic insulated/sealed. It has cut about 25% off his heat bill per degree day. He is 3.5 ton geo. What I am saying here is, get some insulation and you can likely go down a size for you heat pump and save on the bills. Its win-win money well spent.

I would think you could make some adjustments to manual J's or the fuel calc formula to account for the extra insulation.

If you go vertical well closed loop, get the conductive grout fill on the holes. Make sure it's in their quote.

Get a calculated EWT (entering water temp) from the contractor and try to get this as high as you can. 30 Deg EWT seems typ, but if you can get 35 that is better, but it may cost more than its worth as the wells get huge and thats the biggest cost factor.

Size the back up heat toaster packs as small as you can. They will size the system so back up is needed on the coldest days (that is normal and cost effective) but get them as small so they can barely do what they need to do (which is provide back up only, not 100 heat). On the same note, get a t-stat that has programming options so these toaster packs only come on if absolutely needed. ie. if inside temp drops like X degress below set point... This can cause real spikes in energy use if not done right. This was the case at my friends house. Every time his kid pushed temp up, the toaster packs would fire up to meet instant comfort demand. Just kills the bills.

my 2 cents. Best of luck.

Chris

Thanks for the helpful posts - here are the loads from the Manual J load calcs. Can anyone weigh in as to system size for Philadelphia?

Total Heating Required Including Ventilation Air: 34,894 Btuh 34.894 MBH
Total Sensible Gain: 24,013 Btuh 77 %
Total Latent Gain: 7,243 Btuh 23 %
Total Cooling Required Including Ventilation Air: 31,256 Btuh 2.60 Tons (Based On Sensible + Latent)

Looks like a 3 ton 2 stage to me. 2 stage dips too much into supplement heat, costing you $200 a year more in operational costs compared to 3 tons. Plus 2 ton would not be enough for your cooling requirements.

If your going with Forced-Air, I would highly recommend sizing by cooling whether single or two stage equipment. Go by the Book (Manual J, Manual D, Manual S, Manual H).
An experience designer and installer knows how to size single stage and two stage equipment accordingly. With a two stage unit, you can use more heat capacity and yet meet your cooling needs
and still be economical to operate.
 

I think Doc just clarified that a 2 ton ( which would be sized for cooling  - no? ) would cost $200 more then if you sized for heat.


correct me if I am wrong here, but I believe sizing in our area ( philly) should be for heating - since we are a heating dominated climate

3 ton two stage so as to meet the cooling load. There is no such thing as "auxiliary cooling strips"

Generally speaking, in all but the coldest climates, I think most would agree to size for cooling, or at least not oversize by much for cooling. Reasoning is that oversized for cooling is both inefficient (short cycling) and uncomfortable (short cycling causes poor humidity control)

Though a sized for cooling system may fall a bit short for heating, the actual number of hours an auxiliary source is usually quite low. Geo, at least closed loop, is pricey per ton upfront (unlike air source), so spending an extra $3-5k to avoid $50-$100 worth of annual heating cost makes little economic sense, especially given the potential loss of cooling efficiency and comfort.

To follow up on Curt's comments, we are generally cooling +1 here (mid MI) meaning 1 ton more than the cooling load by the time we hit the 92-98% of the heating load we shoot for.
It is not unheard of (though uncommon 'round here) to have a cooling load drive the size selection.

2 ton is not big enough for heating and cooling. 3 tons fits both well and you only need a small amount of aux. 4 ton is too large for cooling and heating.

So if the cooling requirement (outdoor dry bulb 89 with 50% humidity indoor dry bulb 75) can be satisfied with the (2.6) = 3 ton and the heating requirement (outdoor dry bulb 15 with 80% humidity indoor dry bulb 70) requires 4 ton, can the aux strips make up the difference? Are these good numbers to base it on for Philadelphia?

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?


Op and load calcs identify parameters and set points. Savvy contractors add disclaimers. PCT savings is likely more accurate than dollars as load calcs do add fudge.

"Sorry Joe - i guess I'm a bit of a novice here but I really don't understand your last post.... I do however look forward to any direction you can provide."

Apologies I just saw this.......

Perhaps I over abbreviated.
Re whether a cost calc is possible (vs guy who said they didn't know the factors):
Operating cost and load calculations identify set points and the conditions...i.e. heating set point 70* in the envelope identified (by the manual J load calc we provide for our customers) with a design temp of X (in our case about 1*F based on Lansing MI) at a cost of X (kwh or gallon of propane or CF of natural gas etc.)......those are the idendified (not the least bit mysterious parameters).
After the computer spits out the annual op cost of all heating/cooling/hotwater savvy contractors will add caveats i.e. "based on 20 year weather average" "based on 4 persons in the home" "does not include regular house hold energy consumption" (the last one is my favorite; I once had an elderly lady who complained about the incredible jump in her electric bill. She assumed that my op cost prediction was for the total electric consumption of her home with the geo.....even though her electric bill with the propane furnace was $700 and the geo op cost was calculated at $700......as we explored the predictions we stumbled across that disclaimer....).
These disclaimers and parameters are our protection when clients change their behavior.....ie single client gets married to someone with 2 children and experiences a jump in the bill or another common one "since the geo is so cheap we don't have to keep it on 68 anymore (like we told the system designer) I think I'm more comfortable at 72*".....

So they guy that said he didn't know the parameters simply didn't know how to set the parameters.

Finally my last comment was manJ and such calcs are a little liberal (have some fudge factor) and weather varies so while the exact cost of consumption may not be identifiable for years, the percent of savings will be fairly accurate, so if the calcs suggest you will save 50% (vs actual dollars) that is going to be pretty close year in year out inspite of actual dollars spent.

Joe Hardin www.amicontracting.com We Dig Comfort! www.doityourselfgeothermal.com Dig Your Own Comfort!

Aux would make up difference if needed in heating. 3 ton is actually large compared to 92-98% load practices it is a good fit.

Who was that masked engineer , confirmed by DocJ and Joe.???
Curt!

This is exactly what kept me out of trouble, arguing through MANY 1980-2003 :
I looked at the existing fuel usage , estimate system efficiency in the existing residence; and compared to Trane and Carrier's res cooling programs, repeatedly close to m-J...
Simply put:
by 1983 having worked with 27 dealers of HEATING only GT and some direct water-coil 52-edg wells to 56 (no dehum to speak of above 55-deg entering)
...
then recorded 32-36 and 43-46 MBTUh compressors on the heating mostly...
compared to others cooling programs...

Analytical customers pointed out GT-Sized done for operating at zero in Dayton-Cincinnati and to Cleveland and the little cold spot off Marietta, and the 6600 deg days..
and I recorded that.

Cleveland is   35 min off  and 12% to 8% warmer !  where GAS CONTRACTORS got sued for undersizing BY MANUAL J HEATING when ritzy homes dropped to 27 below  in Geauga County... 1994.

So I will ask that home owner for estimated mcf or uty usage.
Check against airflow volume if 8.1/2 ft ceilings
take ~45% to half (vol div by 17 for ~ 3.1/2 air changes per hour..., Tom Dellinger's COMFORT numbeer, TETCO 1993, Col.Ohio)
to check against COOLING CALC (!)
..
2100+ half the old basement~ 2600, if heating... @  under 1300 CFM ~ "3-T"

now in the last size-4-ton r410a Climatemaster, I found only a 40-k compressor... (I understand ratings and also ACCA jumping all over those damp cool homes in the south with overblown high s/t units, just like 54-degree water coils in Dayton, in the 80's S:T of over .88)
so
at for great dehumidifcation, only a MULTISTAGE real 3-Compresor-Tons in the box, if heat load is right, at 380-cfm/ton (like rated's 325-340cfm/ton, on a 3.1/2 ton 2-staging CM equivalent )

BUT: after a first month bill: find a less expensive Supplier by choice in PA now.
Make a better HOME, INSULATED, SEALED IF POSSIBLE; AND
REBUILD FOR A MORE CENTRAL HIGH RETURN AIR FOR ~ 800 CFM
adjust registers in basement to blow downward in a column at very low air flows as possible
(rec center?)

and also look at DUAL compressor 3-staging if you want -10 NO strip heat and thats a 17-18 + 23-24k pair of compressors= 40 k 3.4 real tons, 1st stage ~ 2-rated cooling tons, super efficient...
fully programmable cfm H or C and can make HW on Demand 100% Priority, and lend itself to some radiant additions under Master-Bath flooring or more, easily: ASK for 100% hot water on-demand to compare all things and 3-staging dual compressors.