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HVAC energy consumption

asked 2021-05-27 14:07:16 -0500

Lucille's avatar

updated 2021-05-28 09:04:46 -0500

Hello, I modeled a simple room HVAC system according to the example file, (HVAC template Furnace-DX). How could I find out about HVAC heating (winter months) and cooling (summer months) energy consumption? Is there any variable in the output simply presenting these? The data in the building summery tables for heating and cooling are presenting these or sensible heating and cooling data? I read a lot about sensible heating and cooling and it is confusing for me.

I would like to calculate heating and cooling bill of my model. I'm looking for cooling and heating energy consumption to multiply by electricity and gas price.


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answered 2021-06-07 11:53:32 -0500

Keigo's avatar

updated 2021-06-07 12:48:47 -0500

Your goal is to calculate the zone bill. Then, firstly, please don't use sensible heating and cooling energy. You should use Output:Variable Heating Coil NaturalGas Energy and Cooling Coil Electricity Energy.

I don't know if you are familiar with MEP engineering, but very fundamentally, every heat source has its own efficiency. In this case (FurnaceWithDXSystem.idf), Burner Efficiency of Furnace Heating Coil is 0.8, and COP of DX Cooling Coil is 3.


Heating Coil NaturalGas Energy [J] = Zone Air System Sensible Heating Energy [J] / Burner Efficiency

Cooling Coil Electricity Energy [J] = Zone Air System Sensible Cooling Energy [J] / COP

But the efficiency can vary depending on various factors such as part load ratio and outdoor air temperature, and EnergyPplus automatically calcurates it. So, you should not manually calculate Electricity and NaturalGas Energy from the above equations. Just select Heating Coil NaturalGas Energy and Cooling Coil Electricity Energy.

Secondly, how about Fan Power? The original ExampleFile is a central heating/cooling system with one fan, one cooling coil, one heating coil and three zones (although you might have editted it to a single zone).

If you want to include Fan Electricity Energy to the zone bill, you can add Fan Electricity Energy[J] and Cooling Coil Electricity Energy[J] together. Or, as an easier way, select Output:Meter Electricity:HVAC[J]. This output includes Electricity used in all HVAC equipment such as heat sources, fans and pumps. In this case, there is no pump, so

Electricity:HVAC[J] = Cooling Coil Electricity Energy[J] + Fan Electricity Energy[J]

And for your reference,

Electricity:Facility[J] = Electricity:Building[J] + Electricity:HVAC[J]

Thirdly, you said "In meter output, it combines heating and cooling. I think it calculates also cooling for January and heating for July.", but I don't think so. It's because the original ExampleFile has Control Type Shedule Name in ZoneControl:Thermostat in order to specify when needs to be cooled and when needs to be heated. According to the schedule Zone Control Type Sched, heating is only allowed from Jan to Mar and from Oct to Dec, and cooling is only allowed from Apr to Sep. If you want to set up the thermostat so that both heating and cooling can be available annually, you need to use ThermostatSetpoint:DualSetpoint instead of ThermostatSetpoint:SingleHeatingOrCooling, and you need to use "4" as the schedule .

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Pelase refer to this revised IDF file (the version of EnergyPlus is 9.4.0). I changed the thermostat settings as above. Also, I added Output:Variable and Output:Meter as above. Reporting Frequency is set to Monthly. Furthermore, I added UtilityCost settings. EnergyPlus can calculate and output UtilityCost. Please change Monetary Unit in CurrencyType and Cost per Unit Value or Variable Name (= energy tariff) in UtilityCost:Charge:Simple as you like.

Lastly, your current model seems to have only one zone, but if you want to model the multiple zone and calculate each zone bill later, then you can utilise ... (more)

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answered 2021-05-27 15:23:00 -0500

The HTML results include a breakdown by fuel-type, by end-use in the Annual Building Utility Performance Summary. It will not tell you which season the energy usage occurred (e.g. you won't be able to differentiate general heating energy from summer re-heat), but it is a good simple summary of heating vs. cooling (and other) energy usage.

May be helpful for you to explain a little more about what you are looking for.

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@jbatt I would like to calculate the zone bill. I need to find out how much gas and electricity is used to multiply by the price. I used HVAC template in energy plus examples, (Furnace-DX). I modeled for January and July. There should be a variable showing energy consumption per month. Does sensible heating and cooling variable show this and does it includ electricity?

Lucille's avatar Lucille  ( 2021-05-27 16:22:45 -0500 )edit

Are you looking for heating and cooling usage or total gas and total electrical usage? Do you want this summarized on a zone level or building level? There are a number of options you can use as far as requesting outputs/meters depending on what you are looking for.

jbatt's avatar jbatt  ( 2021-05-27 16:36:01 -0500 )edit

The building just has zone and it is empty, no light no people, nothing, so, whatever electricity or gas is used, it is for heating and cooling. January heating and July cooling. In meter output, it combines heating and cooling. I think it calculates also cooling for January and heating for July. I'm going to use sensible heating and cooling energy and convert them to Kwh and therm to calculate the bill. I could not find any other solution!

Lucille's avatar Lucille  ( 2021-05-27 16:52:03 -0500 )edit

I think sensible heating and cooling energy is the wrong approach. See @Keigo's response. Sensible heating and cooling energy refer to energy that has been delivered to individual zones, but does not refer to how much fuel (natural gas) or electricity (cooling coil energy) was consumed to actually condition the air on the supply side before delivering it to the zones. You are interested in consumption energy because that is what is metered and actually shows up on a bill.

For electricity related to HVAC, I would just use Electricity:HVAC. This should include all fans, coils etc.

sashadf1's avatar sashadf1  ( 2021-06-08 14:36:07 -0500 )edit

You could also find an appropriate variable to represent natural gas consumption across the whole building. I am still confused on what you mean by "zone bill." Does the building only have one zone? If so, there is no need to prorate supply side energy and calculate the percentage that goes into different zones; you can just take the coil variables.

sashadf1's avatar sashadf1  ( 2021-06-08 14:37:48 -0500 )edit

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Asked: 2021-05-27 14:07:16 -0500

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Last updated: Jun 07 '21