[Bldg-sim] eQUEST Hot Water Heater Appendix G Baseline

Tupper, Kendra Kendra.Tupper at sf.fk.com
Tue Jan 8 15:31:07 PST 2008



Did you catch the footnote on the bottom of Table 7.8 that says,
"Instantaneous water heaters with input rates below 200,000 Btu/hr must
comply with [80% thermal efficiency] if the water heater is designed to
heat water to temperatures 180F or higher."?


So, if you're heater does not heat water to 180 F, you can use the EF =
0.62 as your Baseline efficiency in your 90.1 model.  Otherwise, you
must use 80% thermal efficiency as your Baseline.


As far as translating the EF into HIR...


EF include standby losses, while thermal efficiency does not.  In
eQUEST, the HIR does not include standby losses since this is modeled by
specifying the tank volume and UA.  Since the EF of a tankless unit is
essentially zero, it seems perfectly acceptable to model the HIR as 1/EF
and then set the tank volume to zero in eQUEST.


Hope this helps!



Kendra Tupper
405 Howard St. San Francisco, CA 94105
Direct          (415) 402-5840
Email   kendra.tupper at sf.fk.com <mailto:kendra.tupper at sf.fk.com%20> 


From: Andrew McNamara [mailto:amcnamara at brightpower.biz] 
Sent: Tuesday, January 08, 2008 1:24 PM
To: Alex Lekov
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] eQUEST Hot Water Heater Appendix G Baseline


Thank you for your reply.  Your response leads me to two more questions:

1) In the case of an 180 kBTU/h instantaneous heater is it standard
practice to use EF equal to 0.80 (or some other number based on a
"bottom of the heap" instantaneous heater) as you suggested rather than
the 0.62 listed in the standard?

2) How does one translate EF (this or any other) to HIR
(Heat-input-ratio) for use in eQUEST?  Or might it be acceptable to
simply look up the "bottom of the heap" HIR values for instantaneous
heaters and use one of them as a baseline? 

I would appreciate responses from any and all - thanks in advance for
your help!


Andrew McNamara, LEED AP
tel: 212.803.5868
fax: 866.379.8026
cell: 917.974.4499

On 1/8/08, Alex Lekov <ABLekov at lbl.gov> wrote:


It is probably incorrect to baseline the instantaneous water heater
using the current minimum efficiency standard for the residential size
gas instantaneous water heaters (EF=0.62). According to GAMA's
Consumer's Directory of Certified Efficiency Ratings for Heating and
Water Heating Equipment's directory, very few gas instantaneous water
heater models have EF below 0.80.

Alex Lekov, Ph.D., P.E.
office 925-486-6849

Andrew McNamara wrote: 

Hello all,

I am modeling a building with eQUEST that has a tankless, a.k.a.
instantaneous, gas-fired hot water heater.  I am uncertain of how to
baseline the system according to ASHRAE 90.1-2004 Appendix G. The
standard states that for a 180,000 BTU/h system the EF (Energy Factor) =
0.62-0.0019V.  So, I set V equal to zero for the tankless/instantaneous
gas water heater and get an EF =0.62.  

The question I have for everyone is: How do I translate this baseline EF
to HIR (Heat-input-ratio) for eQUEST?  Is there an accepted method for
doing so?  I saw in a previous post from David Eldridge on 3/21/07 that
calculating HIR = 1/EF leads to unreasonably high values for HIR (In my
example, 1/0.62 = 1.61), but I'm having trouble seeing how else to come
up with a baseline.

Thanks in advance for your help.


Andrew McNamara, LEED AP
tel: 212.803.5868
fax: 866.379.8026
cell: 917.974.4499 



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