Trying to find %age energy saving from variety of upgrades in 10K sf multifamily house

I'm trying to figure out %age of energy savings from a variety of upgrades in a 10,000 sf building that has had deferred maintenance and a disfunctional heating system.

I'm using Energy Pro software and trying to figure out what the air flow reduction will be after adding insulation where there is none. The windows are mostly w/o hardware to keep them shut. The forced air system is nonfunctional mostly as there is no way for air to get back to the return air grill (it goes out the windows).

As it is now, the building has de facto electric heat as the forced air hardly functions. Because of this the 30 residents mostly use electric heater. I surmise that after a high quality insulation job and actually sealing the house and HVAC system that there will be little need for electric heat in mild Berkeley, CA.

 

How can I estimate air flow/leakage after the improvements? I got a stunning 27,000 CFM with my blower door in this big leaky 3 story, 10,000 sf house. I know I'm going to improve it drastically if I can sell the job.

 

Also, some of the energy improvements are really deferred maintenance rather than an energy upgrade. The historic steel windows have probably been semi-functional for many decades.

This is a bit more complicated than what I'm used to.

I've gotten bids from a variety of subs to do a quality energy upgrade and need to justify/show improvements and NPV to get a subsidy.

Thanks for any help,

George

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Hello George,

If it were me, I would use the monthly electric bills to determine the average kW for each month's consumption by dividing the monthly kWh by the number of days in the billing period and dividing by 24 hours per day.  I would then determine the average monthly temperature for each monthly read and then plot the average kW verses the average temperature for each month.  The resulting slope of the line during the winter shows the total heat loss for the building that includes ventilation, conduction and existing infiltration.  Calculate the slope of the building's actual heat loss line.  Compare this actual heat loss coefficient to the total predicted heat loss coefficient (kW/F) for the building that includes the condution heat losses, ventilation air and an expected air infiltration rate if the building were properly sealed (0.75 ACH?).  You can then calculate the contribution that the excessive infiltration is having on the building's total heat loss by subtracting the predicted building's total heat loss from the the slope of the actual building's heat loss.

New Infiltration Heat Loss, kW/F = [Expected ACH after air sealing] /hr x [Volume of Home] ft3 x 0.24 BTU/lb F x 0.075 lb/ft3 / 3413 BTU/kW-Hr.

 

Conduction Heat Loss, kW/F = [Wall U-Value] BTU/Hr/Ft2/F x [Wall Area] Ft2 / 3413 BTU/kW-Hr

 

Ventilation Heat Loss , kW/Ft = [Ventilation CFM] Ft3/Min x 0.25 BTU/lb F x 0.075 lb/ft3 x 60 min/Hr / 3413 BTU/kW-Hr

 

The predicted energy savings is simply the difference between the slope of the actual heat loss line and the slope of the predicted heat loss.

Savings Potential, kW/F = Actual kW/F - (New Infiltration Heat Loss + ventilation Heat Loss + Ventilation Heat Loss)

Hi George,

You don't happen to have a spreadsheet handy for those calculations do you? :-)

Here is a spreadsheet that I have for identifying savings using monthly bills and average monthly temperatures.

We documented actual energy savings using this method during our "Reduce Your Use" contest that we conducted here at Chelan County Public Utility District.

 

Jim White

Sr. Energy Conservation Engineer

Attachments:

O.K., forget all of the Engineer jokes! Thank you very much Jim. Engineers rule!

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