Overall energy consumption

RogerR

I need advice on how to calculate expected overall energy consumption. I am looking at buying an apartment in New York City in a century-old brownstone that has just been refurbished with up-to-standard insulation, low-E double glazing, etc. Heating and air-con are by a newly installed gas-powered furnace, equipped with cooling coil and condenser, also new, to provide ducted hot and cold air. Hot water and cooker are gas-powered as well. The report from the consulting engineers estimates that overall the apartment, at just under 1000 sq feet, will consume 1800 therms of gas and 12,500 kWh of electricity per year. With electricity at $0.20 and gas at $2 per therm as they were two years ago this comes to over $6,000 a year. Gas prices today are lower, but it still seems very high. ConEd's website has a home energy calculator that suggests the overall usage should cost around $2,400; however, it doesn't tell you what the calculation is based on.



The engineer's report does not give a breakdown for heating vs other uses. How should I go about calculating whether this is a reasonable energy usage myself?

Mark Eatherton

Theoretical versus reality...

The ONLY way to even come close is to perform an actual heat loss, and a blower door test to determine infiltration. Once this is done, there are programs out there that will calculate your annual heating consumption based on localized weather data.



That is JUST for heating. Then there is DHW. THe national average is 20 gallons per person per day. The BTU's required depends on the temperature differential of the water. And that changes on a seasonal basis.



The calculation of electrical consumption is a LOT more tricky. Just knowing the lights in the house are one thing. Knowing how long they will be on is critical. The run time of refrigerators/freezers is also a function of variables.



The last thing a consulting engineer wants to do is estimate low and have you come back on them, so they are typically high in their estimates.



The other BIG factor in determining the heating demand, is the isolated mass potential, the solar and internal gain potentials, and how the system is operated, as well as the efficiency of the heating appliance.



And then there is the potential cooling loads (assuming you have a cooling system) that need to be considered.



SO, as you can see, it's not easy being Green (Thanks Kermit :-)) And its even harder to estimate how much green you will lose in the process...



ME

STEVEusaPA

there's a 1000 ways....

but arent they just really guessing?  They consulting engineer isnt going to help you with utilities if he's wrong, is he? Was this a brownstone converted to apts, or was this already converted and they upgraded.  If its just upgrades, and if it were me, I would ask for a year's worth of bills from the last owner.  Now granted, that was before all the work was done, but at least you'll know what the maximum would/could be.  It of course also depends how your set up.  Are you the only apt on the floor?  Who's above/belownext to you, etc.  Are they all occupied? If ya get someone below you who keeps it at 80 in the winter, that will help.  If you get lots of sunlight in the summer, that could hurt.

I would lean more towards the engineer then ConEd.  But you know what they say about figures..........

If you do get the place, stop back in a year from now and let us know how the engineer did.  I for one would love to know.

Gordy

All true

 Roger,



   I would like to know what size family the calculations were based on. That is a biggy. Obviously 1 person is going to be a heck of a lot cheaper than 4. 1 persons energy consumption habits are much easier to manage than 4, especially when it comes to hot water, and the thermostat. If 3 of the 4 are women it all just went up.



Gordy



 

Long Beach Ed

New York

New York has a "Truth in Heating" Law which requires utilities to provide energy usage history to prospective property buyers and renters. 



Here's the legislation:

http://law.justia.com/codes/new-york/2010/eng/article-17/17-103/



Other states may have similar laws. 



It's a start...

D107

Costs

HO here; projected gas usage seems WAY over-estimated. I have a 2000ft 1924 house in Westchester NY with a 30 year-old 4x oversized gas boiler, gas drier, gas hwh and gas range that at worst some years ago--before added wall and rim joist insulation, fireplace cap, weathersealing, etc.--reached 1400 therms. Now it's down to about 1150 therms, incl. 950 for heating. Admittedly we keep house at 65deg.day, 63 night, so keep it at 70 and you'd use more, but your space is half, with new windows and insulation and your climate is slightly warmer.  My highest usage is about 245 therms for a really cold month; highest winter electric month is about 340KWH, highest summer month is 1000KWH.(really hot summer). (Two residents.) If I had a modcon and foam-sealed, unvented attic, new windows, that would be a closer comparison to your conditions.

Gordy

compare

I also have 2000 sf Midwest.

910 therms 262 of which is for hot water last year family of 4. T stat at 72* never set back. 6487 HDD.



I Trump the KWs though. But I have a pool, 2 freezers, extra fridge, electric dryer HE,Landscape lighting, and window ac for the summer. So highest is about 4000KW, and lowest 800KW. probably 20000kw a year.



So as you can see Roger it DEPENDS!



Gordy