Revision history [back]

Hi,

I am working with DOE Commercial Reference Building models to do some simplified, high-level analysis of what might be expected to be 'typical' levels of the coincidence of the load on HVAC systems in commercial buildings and utility system (transmission grid) peak demand. For the case described here, I am running the post-1980 Full Service Restaurant model for the Houston weather zone as developed, using EnergyPlus 7.2 (latest version in which models are available on DOE website).

My issue is that the models appear to be telling me something impossible: that cooling electricity energy use in several hours (77 hours, when run using TMY3 data) exceeds the amount of electricity the HVAC systems should draw when fully loaded. To arrive at this conclusion I obtain hourly Cooling:Electricity from the Meter file, and I obtain the HVAC systems capacities as estimated from the sizing run from the Cooling Coils table in the Equipment Summary of the HTML Tabular output report.

According to the .mtd file, this is what is rolled up on the Cooling:Electricity meter:

For Meter=Cooling:Electricity [J], ResourceType=Electricity, EndUse=Cooling, contents are: PSZ-AC_2:2_COOLC DXCOIL:DX Cooling Coil Electric Consumption PSZ-AC_1:1_COOLC DXCOIL:DX Cooling Coil Electric Consumption PSZ-AC_2:2_COOLC DXCOIL:DX Cooling Coil Crankcase Heater Consumption

For capacity from the sizing run, I use the sum of the Nominal Total Capacity of the two units as reported in the Cooling Coils table of the Equipment Summary (Table report). To convert this (output) capacity to input demand, I divide by the COP.

My basic question is, how can this happen? Have I misunderstood/misused either the Nominal Total Capacity of the cooling coils from the Equipment Summary or the Cooling:Electricity meter 8,760 data as data sources for this comparison?

Further confusing matters, given use of a cooling sizing factor (Sizing:Parameters object) of 1.2, I would expect the maximum ratio of hourly cooling energy use (demand) to capacity to be closer to 1/1.2. Design day conditions used are standard - ASHRAE Fundamentals 0.4% design day, and I've run with both TMY2 and TMY3 data (FWIW, it's only with the TMY3 that I get demand in excess of capacity - with TMY2 I do get a coincidence factor less than 1, but not much less - 0.96).

Any insights would be greatly appreciated.

Hi,

I am working with DOE Commercial Reference Building models to do some simplified, high-level analysis of what might be expected to be 'typical' levels of the coincidence of the load on HVAC systems in commercial buildings and utility system (transmission grid) peak demand. For the case described here, I am running the post-1980 Full Service Restaurant model for the Houston weather zone as developed, using EnergyPlus 7.2 (latest version in which models are available on DOE website).

My issue is that the models appear to be telling me something impossible: that cooling electricity energy use in several hours (77 hours, when run using TMY3 data) exceeds the amount of electricity the HVAC systems should draw when fully loaded. To arrive at this conclusion I obtain hourly Cooling:Electricity from the Meter file, and I obtain the HVAC systems capacities as estimated from the sizing run from the Cooling Coils table in the Equipment Summary of the HTML Tabular output report.

According to the .mtd file, this is what is rolled up on the Cooling:Electricity meter:

For Meter=Cooling:Electricity [J], ResourceType=Electricity, EndUse=Cooling, contents are: PSZ-AC_2:2_COOLC DXCOIL:DX Cooling Coil Electric Consumption PSZ-AC_1:1_COOLC DXCOIL:DX Cooling Coil Electric Consumption PSZ-AC_2:2_COOLC DXCOIL:DX Cooling Coil Crankcase Heater Consumption

For capacity from the sizing run, I use the sum of the Nominal Total Capacity of the two units as reported in the Cooling Coils table of the Equipment Summary (Table report). To convert this (output) capacity to input demand, I divide by the COP.

My basic question is, how can this happen? Have I misunderstood/misused either the Nominal Total Capacity of the cooling coils from the Equipment Summary or the Cooling:Electricity meter 8,760 data as data sources for this comparison?

Further confusing matters, given use of a cooling sizing factor (Sizing:Parameters object) of 1.2, I would expect the maximum ratio of hourly cooling energy use (demand) to capacity to be closer to 1/1.2. Design day conditions used are standard - ASHRAE Fundamentals 0.4% design day, and I've run with both TMY2 and TMY3 data (FWIW, it's only with the TMY3 that I get demand in excess of capacity - with TMY2 I do get a coincidence factor less than 1, but not much less - 0.96).

Any insights would be greatly appreciated.