Unmet Hours

DHW end USE - DETAILED HVAC

asked Nov 12

rchrd73
1

updated Nov 12

Aaron Boranian

14315 ●89 ●25 http://bigladdersoftware.com/

Hey everybody,

I am doing my thesis, which contains calculations of DHW usage. I am trying to figure out, how is calculated the end use of water systems. I have DETAILED HVAC. Just simple electric loop with one outlet and one DHW tank. When I run short simulation (1-2days) and cross check with simple Q = m * c * t (J) calculation, it doesnt get same number, so I suppose there is another way.. Do anybody know how it is calculated?

Comments

@rchrd73 by "Detailed HVAC", do you mean you're defining individual HVAC components in the EnergyPlus IDF instead of using HVAC templates, or are you using "Detailed HVAC" mode in an EnergyPlus interface (e.g., DesignBuilder)?

Aaron Boranian ( Nov 12 )

I am using detailed HVAC mode in Designbuilder.

rchrd73 ( Nov 12 )

Hi, Can you please be more specific? Do you have a water heater with electric resistance heating? Is that coil autosized? is the tank size autosized? What is the setpoint temperature? the end use water systems is the energy of the fuel source consumed (electricity, natural gas). This is a function of the efficiency of the component and the load.

Greg Estep ( Nov 12 )

Hi, I just have the simpliest, default DHW loop with electric boiler in Designbuilder. Everything is set to default and autosize. Setpoint for water is 55 degrees.

rchrd73 ( Nov 12 )

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2 Answers

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answered Nov 13

Aaron Boranian

14315 ●89 ●25 http://bigladdersoftware.com/

DesignBuilder is an EnergyPlus interface, so for calculation questions like this it's usually best to consult the EnergyPlus documentation, specifically the Engineering Reference. For water heaters, there are many components to the energy balance:

heat added by heating element ("Water Systems" end use that you're focusing on)
heat added due to on/off cycling parasitic loads
heat added OR lost to air surrounding tank (aka ambient)
heat added OR lost to water connections in & out of tank ("use side" going to DHW draws or "source side" if hot water provided to tank by solar thermal collectors or something similar)

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answered Nov 18

Tokarzewski

524 ●10 ●8

There are two methods for defining DHW consumption depending on the Detailed HVAC activity data setting defined in Model Options. I attach one link and screenshots below for reference.

https://designbuilder.co.uk/helpv7.3/...

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