Modelling oil-fired systems with different COPs in Designbuilder (Simple HVAC)

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Hello All,
I'm trying to compare two oil boilers with different COPs. One is 55% efficient and the other 82% efficient. I'm using the Simple HVAC model, however the results for Zone heating (kWh) do not change for the two boilers. All other parameters of the building remain the same. One would expect the lower efficiency boiler to perform more leading to a higher energy consumption to a higher efficiency boiler. Has anyone come across this in simulations? Can't understand what I am doing incorrectly.

Regards,

Apeksha Gupta

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I think your issue is that Design Builder simple HVAC uses Energy Plus
"ideal loads" HVAC, and that the comparison you are doing requires you to
model an actual HVAC system. Try to use the detailed, or at the least
compact HAVC and see if your problem is solved.

CleanTech Analytics's picture
Joined: 2012-02-09
Reputation: -1

Please give us your .INP and .PD2 files. How you can run oil in a "simple" HVAC model is beyond me. You cannot be in the Wizard.

John R. Aulbach, PE, CEM

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This is in reference Energy Plus (the modern simulation engine supported by
the USDOE) and an interface called "Design Builder", not the legacy DOE2
engine and eQuest freeware interface, so INP and PD2 files are not
possible. If you export your IDF or send your DSB file than I could take a
look for you..

CleanTech Analytics's picture
Joined: 2012-02-09
Reputation: -1

He?s using Designbuilder, so don?t worry!

James V Dirkes II, PE, BEMP, LEED AP

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Joined: 2011-10-02
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Apeksha,

It might just be a case of misinterpreting the results...I would advise
checking the "simulation detailed results" descriptions in the help file.
The zone heating is the heat input to the zone from the zone emitters, not
the energy consumed by the plant. You should find that your energy
consumption at building level changes with a change in plant efficiency
(providing all else remains equal).

Hope that helps,

David Cocking

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Hi David,
Zone heating is in fact the heating demand of the building that is unaffected by the plant's efficiency as pointed out by Jim Dirkes. When I looked at the heat generation results they were varying for different efficiencies with all other parameters remaining equal.

Thanks,

Apeksha Gupta

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Hi Apeksha,

I think you're saying the same thing in a different way. The heating demand of the building is met by the zone emitters (after any contributions from internal and external gains), and you wouldn?t expect the zone heating values to change with variations in boiler efficiency. The heat output from the heating plant is that required to meet the heating load; it is unaffected by efficiency but the amount of fuel consumed meeting that output will clearly vary with efficiency.

Hope that helps,

David Cocking

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Hello All,
Thank you all very much for this interesting input. Made me realise what the 'Zone Heating' in Designbuilder suggests against the 'Heat generated' by the heating system.

Regards,

Apeksha Gupta

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