Changing DHW Schedule Does not Change the Gas Consumption

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Hello Guys,
I am changing the fraction in the Domestics Hot Water (DHW) schedules in eQUEST but the gas consumption is not changing. Does anybody encountered something like that?
I spent a lot of time trying to fix it but I could not. Your help will be highly appreciated.
Thank you.
Ahmad

Ahmad Fraij's picture
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I am not aware of a general issue with DHW in eQUEST with regards to the schedules so I suspect it is a project specific issue ? at which point sharing the .inp may be helpful. I have been surprised at the impact of the UA value in the DHW heater on the heater?s efficiency, but as the loads change, the natural gas input will also.

Quick checks:

- Are the schedules linked as you expect? Daily->weekly->annual->DHW Loop Process Load

- Are the changes being masked by other gas uses? i.e. check the PS-H report in the .sim for the DHW heater ? is the load and response there changing?

- Check the Process T of your DHW loop. If it is lower than the DHW loop temperature, the DHW flow is ?mixed? at the tap with the incoming water temperature reducing the DHW loop flow. Perhaps this is set much too low?

[cid:image002.png at 01D7B373.97709DF0]

Brian

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Thanks Brian for your help.
I checked the PS-H report and found that the DHW loop flow and the coil load is infinity as per the screen shot below. Do you think this is the problem? what could be the reason?
Looking forward for your advice.
Regards

On Monday, September 27, 2021, 09:47:17 PM GMT+10, Brian Fountain wrote:

I am not aware of a general issue with DHW in eQUEST with regards to the schedules so I suspect it is a project specific issue ? at which point sharing the .inp may be helpful.? I have been surprised at the impact of the UA value in the DHW heater on the heater?s efficiency, but as the loads change, the natural gas input will also.

?

Quick checks:

-?????????Are the schedules linked as you expect? Daily->weekly->annual->DHW Loop Process Load

-?????????Are the changes being masked by other gas uses?? i.e. check the PS-H report in the .sim for the DHW heater ? is the load and response there changing?

-?????????Check the Process T of your DHW loop.? If it is lower than the DHW loop temperature, the DHW flow is ?mixed? at the tap with the incoming water temperature reducing the DHW loop flow.? Perhaps this is set much too low?

?

?

?

Brian

?

Ahmad Fraij's picture
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Hi Ahmad,
My guess is that you have entered the capacity incorrectly ? a common mistake in eQUEST for boilers and DHW heaters. The units are million Btus/hour, written as MBtu/h, but MBtu/h is often interpreted the same as kBtu/h. (Boiler manufacturers often list capacities in MBH by which they mean thousands of btus per hour.)
For example, a typical 50 gallon tank water heater with a 4.5 kW electric heating element would have a capacity of (4.5kW)*(3413Btu/h-kW)/(1000000Btu/h-Mbtu/h) = 0.015 MBtu/h
Regards,
~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP
Senior Energy Engineer
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