calculate cost to heat or cool house

[doogan123]

Hi all

I have a simple question (Or maybe not). How can i determine the cost to heat or cool my house. I assume I need many numbers. So i guess I am asking 2 things really

what specific numbers i need to calculate and then how to calculate
HEating will be a duel fuel, hp + boiler

I assume i need

Heating BTU's
cooling btu's
Cost of Electricity
cost of propane
efficiency of Heatpump
efficiency of boiler
output of heatpump/boiler??

what else?

Thanks

[beenthere]

BTU loss and gain of house.
Ratings of equipment selected.
HP balance point.
Bin data for your area.
Rates of electric and LP.

[doogan123]

Let me rephrase this i think - or ask a variation that may make more sense.

I have seen the posts and responses where the knowledgable folks on here have shown that with a heatpump - it costs significantly less to heat 1 mm btu of heat Vs using propane or oil etc...

What i am trying to figure out how long the payback is in going with the hybrid system Vs a the regular boiler. I finally have settled on a contractor to do a hybrid HP/Gas furnace system and a contractor that can do a hydronic gas fired boiler system. There is a 25 % difference in cost ( taking into account using the boiler for indirect hot water With the boiler system Vs installing a Gas fired hot water tank with hybrid system). Hybrid is the more expensive system

So how long will it take to get payback of that 25% going with the hybrid

Am I making sense?

thanks

[cem-bsee]

so ask the contractor for the hybrid sys to justify his premium--
-- what does he think the time frame will be --

[smokin68]

Let me rephrase this i think - or ask a variation that may make more sense.

I have seen the posts and responses where the knowledgable folks on here have shown that with a heatpump - it costs significantly less to heat 1 mm btu of heat Vs using propane or oil etc...

What i am trying to figure out how long the payback is in going with the hybrid system Vs a the regular boiler. I finally have settled on a contractor to do a hybrid HP/Gas furnace system and a contractor that can do a hydronic gas fired boiler system. There is a 25 % difference in cost ( taking into account using the boiler for indirect hot water With the boiler system Vs installing a Gas fired hot water tank with hybrid system). Hybrid is the more expensive system

So how long will it take to get payback of that 25% going with the hybrid

Am I making sense?

thanks

You have to have all your costs in order to calculate anything. In some areas,a heatpump might not be a wise choice if your electricity is high and your weather is cold...a heatpump loses it's capacity the colder it gets. When the heatpump's output goes below the balance point of your house(the temp at which the heatpump needs help to heat your home), you will have to run another heat source besides the heatpump. The best way for you to find out pay-back is to ask your local contractor(s).....ask them both what the payback will be.

[larobj63]

You will have central cooling with the heat pump system, and you won't with the hydronic heating system.

That alone might be worth the 25% upcharge.

Although I will say, all else being equal, hydronic heat is "nicer" than forced air, in terms of comfort and quite. But cetral cooling sure is nicer than window bangers.

As far as the payback calc - beenthere stated the info you need. In a general sence (most areas), heat pumps are usually cheaper to run than propane or oil, and natural gas is generally the cheapest of any fuel. But, as I'm sure you've gathered, this varies by locality, and this variation effects the payback.

[doogan123]

BTU loss and gain of house.
Ratings of equipment selected.
HP balance point.
Bin data for your area.
Rates of electric and LP.

I am on the final stretch on selecting a HVAC system. As mentioned i have 2 systems competing at this time. On is 25% more than the other. The premium system is a bryant evolution hybrid. I think its a fantastic system. (15 Seer, 11.7 EER The second is a straight hydro Air with AC. Boiler would be a Buderus Propane GB142/30. 94% AFUE

My last hurdle is to determine ( or closely estimate) the operating cost of each and the difference. I am trying to determine how long the payback will take on the premium system vs the Hydro.

Beenthere - To respond to your items ( and hopefully you can help again ) I have compiled the below. I am unable to get everything but i hope its sufficient

Electric Rate - 11 cents/KWH ( Fixed for 2009)
Propane - 2.80
Oil - 3.05
HP Balance point - 32 Deg
Bin Data - not sure what this is - however i got the average Heating degree days - 4804 and cooling degree day - 1190 for my area. Let me know if i need to get something different
Ratings of equipment. I have not identified this. Cannot locate. I have a call into my contractor - however if this helps - the bryant furnace (2) are model # 355BAV042060
The bryant HP (2) are model # 286AWA036000. 15 Seer, 11.5 EER

For the second system - the heating is a buderus GB 142 / 30. First company Air handlers 24MBXB-HW (2)

So - I would love to be able to understand how to calculate the operating costs. What else am i missing to do this?

I have this asked of both contractors - however I need to be able to independently understand how to get this to move forward comfortably.

Thanks guys

[beenthere]

Heating Degree days doesn't give you enough info.
Unless you have the fuel consumption records for the previous year.

Bin Data, is how many hours a year at what temps.
EG: 641 hours between 65 and 60, 581 hours betweent 60 and 55, 780 hours between 55 and 50, etc.
Then with the load clac, you can determine how much heat you need total for the hours at each of those temp bins, and determine seasonal cost from there.

With your current rates.
If you need 60,000,000 BTUs for the heating season.
At the rates you posted.

HP at an averaged COP of 2.5 providing 70%, elec Aux providing 30% = $1,121.59
HP at an averaged COP of 2.7 providing 55%, 94% LP providing 45% = $1,268.11(LP hot air furnace)
HP at an averaged COP of 2.5 providing 70%, 94% LP providing 30% = $1,124.25(LP boiler with hydro coil)
HP at an averaged COP of 2.7 providing 55%, 82% Oil providing 45% = $1,111.25(Oil hot air furnace)
HP at an averaged COP of 2.5 providing 70%, 82% Oil providing 30% = $1,019.68(Oil boiler with hydro coil)
LP only at 94% = $1,942.65
Oil only at 82% = $1,594.08

Your house may need more or less heat.
But, the difference in operating cost, will still be the same ratio as the above example.

[doogan123]

THanks - this is the comparison i was looking for.

I just realised that I never posted my heat loss - Sorry it was very late....

Heat loss is 64287 BTU
Cooling load is 42280 BTU

How did you get to 60 MM BTU - was this just an estimate?. Now that i have posted the heat loss - can this ce calculated?

Thank

[Rhizzlebop]

OP, I don't think you need beenthere to recalculate this for you.

If he guessed 60, and your heatloss is 64, that's pretty D&^% close. He already stated that it would be the same % ratio differences based on your heat loss, so just add about 7% to all those yearly costs, and there you go.

[doogan123]

ok - so Beenthere used 60 Million BTU as what needed for the heating season to calculate. But the heatloss is 64 Thousand BTU (64,287).

How should corrolate hese 2 numbers - I guess If I understood this i can figure out the rest?

What i the heat loss calculation typically measured in - is it per day?, Per hour etc?

[gary_g]

What i the heat loss calculation typically measured in - is it per day?, Per hour etc?

BTU per hour.

Take care.

[gary_g]

HP at an averaged COP of 2.5 providing 70%, elec Aux providing 30% = $1,121.59
HP at an averaged COP of 2.7 providing 55%, 94% LP providing 45% = $1,268.11(LP hot air furnace)
HP at an averaged COP of 2.5 providing 70%, 94% LP providing 30% = $1,124.25(LP boiler with hydro coil)
HP at an averaged COP of 2.7 providing 55%, 82% Oil providing 45% = $1,111.25(Oil hot air furnace)
HP at an averaged COP of 2.5 providing 70%, 82% Oil providing 30% = $1,019.68(Oil boiler with hydro coil)

The 2.7 and 2.5 COP seem a little low. This was based on the Bryant model provided and the bin temps?

He stated his balance point was 32F.

My Goodman 3 ton has a COP of 3.25 at 35F.

Thanx and take care.

[Rhizzlebop]

I would agree they seem a little low, but beenthere usually knows what he's talking about.

As far as doing the calculation, the rates, and intervals are already accounted for, all you need to do is add that % to those total dollar numbers.

If he had 60 and you're saying 64, then its about 6.5% higher cost.

Take his 1200 dollar number, or whatever they were and add 6.5% (I think 6.25% to be exact.

So, take 1200*1.0625 = 1275. simple


Yes, the 64 is per hour, but if all those energy dollars given include all that based on 60 per hour, then its like saying, for every hour, its just 6.25% more, so overall, 6.25% more than the big number.

[beenthere]

COP, although important. Has more effect on heat pumps with electric aux heat, then it does on dual fuel systems. That are locked out at a balance point that makes them switch to the more expensive heat source as sole source of heat.

Only redid two at a COP of 3.5

HP at an averaged COP of 2.5 providing 70%, elec Aux providing 30% = $1,121.59
HP at an averaged COP of 3.5 providing 70%, elec Aux providing 30% = $966.89
Difference of 14%.

HP at an averaged COP of 2.7 providing 55%, 94% LP providing 45% = $1,268.11(LP hot air furnace)
HP at an averaged COP of 3.5 providing 55%, 94% LP providing 45% = $1,180.87(LP hot air furnace)
Difference of 7%.

I picked a arbitrary total yearly house heat load of 60,000,000, just because its an easy number to work with, and representative of many mid sized homes.

I also picked arbitrary COP's because I don't have extended data on his equipment, and I don't know his weather pattern. So I choose a safe COP so as not to show an excessively false low operating cost.


You just wanted an idea of how long it would take to get the 25% additional cost back.
If you know what your total heating fuel use was for last year. You can use that with my numbers to get a fairly accurate idea of ROI time. Just by doing the percents.

For sizing purposes, heat loss and gain are calculated by the hour.

[doogan123]

COP, although important. Has more effect on heat pumps with electric aux heat, then it does on dual fuel systems. That are locked out at a balance point that makes them switch to the more expensive heat source as sole source of heat.

Only redid two at a COP of 3.5

HP at an averaged COP of 2.5 providing 70%, elec Aux providing 30% = $1,121.59
HP at an averaged COP of 3.5 providing 70%, elec Aux providing 30% = $966.89
Difference of 14%.

HP at an averaged COP of 2.7 providing 55%, 94% LP providing 45% = $1,268.11(LP hot air furnace)
HP at an averaged COP of 3.5 providing 55%, 94% LP providing 45% = $1,180.87(LP hot air furnace)
Difference of 7%.

I picked a arbitrary total yearly house heat load of 60,000,000, just because its an easy number to work with, and representative of many mid sized homes.

I also picked arbitrary COP's because I don't have extended data on his equipment, and I don't know his weather pattern. So I choose a safe COP so as not to show an excessively false low operating cost.


You just wanted an idea of how long it would take to get the 25% additional cost back.
If you know what your total heating fuel use was for last year. You can use that with my numbers to get a fairly accurate idea of ROI time. Just by doing the percents.

For sizing purposes, heat loss and gain are calculated by the hour.

Beenthere - thanks for your the information.

Can i calculate my seasonal heat load from the heat load ( 64K BTU/Hr) and heating degree days (4808). If not what do i need to calculate it

Thanks

[larobj63]

Beenthere - thanks for your the information.

Can i calculate my seasonal heat load from the heat load ( 64K BTU/Hr) and heating degree days (4808). If not what do i need to calculate it

Thanks

Do you have any historical fuel usage? A years worth of fuel (in btus) multiplied by the existing system efficiency will yield the annual heat load. The wild card is the existing equipment efficiencey - may be hard to get that number right on. But you can get pretty close - a standard efficiency boiler or furnace might be 78% or so...

[doogan123]

Unfortunatly I do not - I had an ancient system that sucked in fuel and shot it up the chimney.

probabally 1500-200- Gallons of Oil if i would guess..

My boiler was .. 50-60 years old - a real gem.

[larobj63]

Unfortunatly I do not - I had an ancient system that sucked in fuel and shot it up the chimney.

probabally 1500-200- Gallons of Oil if i would guess..

So account for the "shot it up the chimney" by adjusting the overall system efficieny.

Here's an example - play with the numbers as you like.

(2000 gal / yr) (139,000 btu / gal) (65% overall efficiency) = 180,700,000 btu / yr.

Seems highish - domestic hot water also oil fired?

[beenthere]

Beenthere - thanks for your the information.

Can i calculate my seasonal heat load from the heat load ( 64K BTU/Hr) and heating degree days (4808). If not what do i need to calculate it

Thanks

Best way is using the bin data.
What major cities are you near.
I may have the bins for it.