[Equest-users] my math on DWH efficiency?

James Hansen JHANSEN at ghtltd.com
Wed Jul 6 08:30:41 PDT 2011


I had a question about calculating baseline 90.1 efficiency for electric
DWHs (tank type).

 

Based on Table 7.8, my efficiency needs to be SL = 20 + 35*sqrt(V) at a
70 degree delta T between water and ambient, where SL is the standby
loss in btuh, and V is the volume of the tank.

 

If, in my proposed model, I have a 240 gallon tank (meaning my baseline
has the same volume), it would appear that the maximum standby loss at a
70 degree delta should be 562 btuh [20 + 35 * sqrt(240)]

 

Since eQuest calculates the heat loss by multiplying the UA (thermal
conductivity of storage tank) by the tank, it would appear that my UA
for this particular example would be 562 / (70*240), or 0.0334.

 

That way, at a 70 degree delta, the heat loss (SL) would be 0.0334
Btu/hr-gal-F * 240 gallons * 70 F = 562 btuh

 

Does that sound about right?  

 

Thanks to anyone that has a quick chance to review!

 

GHT Limited
James Hansen, PE, LEED AP

Senior Associate

1010 N. Glebe Rd, Suite 200

Arlington, VA  22201-4749

703-338-5754 (Cell)

703-243-1200 (Office)

703-276-1376 (Fax)

www.ghtltd.com <http://www.ghtltd.com/> 

 

 



The information contained in this communication is confidential, may be privileged, and is intended only for the use of the addressee.  It is the property of GHT Limited.  Unauthorized use, disclosure or copying of this communication or any part thereof is strictly prohibited and may be unlawful.  If you have received this communication in error, please notify me immediately by return e-mail or by e-mail to ght at ghtltd.com, and destroy this communication and all copies thereof, including all attachments.  Thank you.



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