Unrealistic service water heating load

asked 2017-09-13 19:43:04 -0600

gsuscalo
271 ●1 ●6

updated 2017-09-14 12:58:05 -0600

I'm currently using Openstudio 1.14 on a windows 10 computer. I'm having problems with the service water heating load- when I follow the OS 0.9 online tutorial instructions for adding fixtures and a service water loop, I get absurdly high natural gas loads for the water heater (almost half the building energy load for two 'bathrooms' with 4 fixtures each- but online sources say service water load for my type of building should only be 5-10% of building energy use). Does anyone have any idea why this might be happening? If I try to auto-size the tank volume or service water heater capacity the simulation has a 'fatal error' and fails- that's the only thing I've tried so far.

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Assuming you have the max flow rate for the fixture, also look at the flow rate fractional schedule. This should typically be much lower than the fractional usage schedule for lights or equipment.

David Goldwasser ( 2017-09-13 22:30:37 -0600 )edit

This is at least part of the story- I just drew the fractional schedules down and got a significant change.

gsuscalo ( 2017-09-14 15:14:42 -0600 )edit

Can't help more without information on what the WaterHeater Mixed object looks like. An unlikely culprit would be unusually cold water coming into the system, or a pump that is using too much energy.

David Goldwasser ( 2017-09-19 10:31:08 -0600 )edit

Thanks, I think it was the flow rate of the fixtures (now @ the 'baseline' levels specified in the LEEDv4 reference), the fractional use schedule, and the temperature (now set to a more 'moderate' temperature for hand-washing).

gsuscalo ( 2017-09-28 16:35:00 -0600 )edit

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answered 2017-09-19 13:40:26 -0600

gsuscalo
271 ●1 ●6

David, here's the settings for the water heater: image description

image description

Since I managed to bring the service water natural gas load down a bit by changing the fractional use schedules, the water connections now correspond to two bathrooms w/ four 1-gpm sinks each and a cafe with one 2.2-gpm sink. I also brought loads down again by creating new temperature schedules & applying them to the definitions for my 'bathroom' and 'cafe' fixtures (e.g assume constant 40C hand-washing temperature). So the results might be realistic enough now...but if you see any huge, obvious problems with the water heater loop; feel free to point them out.