[Equest-users] DHW Loads - What is the Process Flow in gpm?

[Sundharam, Premnath]

Folks,

 

I am trying to understand modeling the DHW system in eQuest. I searched
through the list archives for posts. I found some information but still
am not clear.

 

Our project has the following:

1.       3 heaters per DHW loop and 1 DHW loop per building for FOUR
buildings.

2.       Total occupants = 1526 and shower load is the major load
(lavatories are negligible) 

3.       We use a 1.2 gpm shower head. 

4.       We estimate a 12 min shower per day per occupant as the load
and the load does not vary through the year. 

5.       Hot water supply temperature is 105 F

6.       Our storage gas water heaters are 92% efficient.

7.       Our potable water comes from a reservoir and so I built a DHW
inlet water temperature schedule that reflects the changes per month

 

We also have a solar thermal system that using RETSCREEN we figured out
that it saves about 60% of the total hot water consumption.

 

Modeling attempt 1:

1.       I used one single loop and one heater for the entire campus.

2.       On the below screen shot for the DHW loop what is the Process
Flow in gpm?

a.       Do I calculate it as below?

                                                               i.
Process flow = (1526 occupants x 1.2 gpm x 12 min per day) / (24 hours x
60 mins) = 15.26 gpm

                                                             ii.
And then assign a DHW_schedule that has 1.0 as the multiplier for all
the hours in the year

b.      Or do I calculate it as below?

                                                               i.
Process flow = 1526 occupants x 1.2 gpm x 12 min per day / 60 mins per
hour = 366.24 gpm

                                                             ii.
And then assign a DHW_schedule that has basically "0" as the multiplier
for all the hours except "0.5" for 6 am to 7 am and "0.5" for 5 pm to 6
pm - this way I am allowing half of the occupants to take shower in the
morning and the other half in the evening and the rest of the hours
there is no demand - this close to reality!

c.       Or do I count all the shower heads I have and figure out the
total gpm of the heads?

 

Screenshots of the inputs on the Loop:

 

 

 

 

Problems:

If I input the process flow as 15.26 gpm, eQuest is calculating the
total DHW energy consumption as 5,315 Million BTU but our hand calcs
only shows 2,298 Million BTUs.

 

So if any of you have any suggestions on getting the DHW load correct, I
would really appreciate that.

 

Also on the Solar Side, what is the best way to simulate this?

 

Again many thanks.

Prem

 

 

 

 

Premnath Sundharam, Assoc. AIA, LEED AP

Architectural Designer  |  Senior Associate

psundharam at dlrgroup.com

DLR Group

Architecture  Engineering  Planning  Interiors

o: 602/381-8580
6225 North 24th Street, Suite 250  Phoenix, AZ  85016-2020
dlrgroup.com <http://www.dlrgroup.com/>   |  listen.DESIGN.deliver
 
 

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