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Fan heat gain to cooling coil sizing in E+ 9.0.1

asked 2018-10-18 22:36:49 -0500

zahro's avatar

updated 2018-10-18 22:48:08 -0500


I am using recently updated 9.0.1 energy plus version, which this link said that the calculation of cooling coil component sizing is now accounting for fan heat gain contribution. I tried to compare my sizing calculation result with E+ 8.9 and 9.0.1 to look at the impact of fan heat gain into the sizing calculation. I am using HVAC Template VRF system which connected with one DOAS system that serves all 10 conditioned room in the building.

I looked at these variables : 1. VRF Air Terminal total cooling rate 2. VRF Cooling Coil total cooling rate 3. Fan heat gain to the air 4. Component sizing summary

From my understanding, the cooling coil cooling rate should account for zone cooling load + fan heat gain, so the calculation should be: VRF Cooling coil = VRF Air terminal + Fan heat gain in the hourly variable. I checked this number and there is a difference around 1% with VRF Cooling coil, and the VRF Cooling Coil number is always bigger than the sum of Air terminal and Fan heat gain. However, I did not recognize much difference in the sizing result from both versions. My fan heat gain rate number is around 20 - 120 W and the difference of sizing result is only 2-20 W.

How does Energy plus calculate the fan heat gain impact into the cooling coil size? Is it better for me to use the equipment which has the capacity of [cooling coil size + fan heat gain] or the sizing result from 9.0.1 E+ already calculated it for me and I only need to take the coil sizing?

Thank you

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answered 2018-10-19 08:04:19 -0500

updated 2018-10-19 08:17:29 -0500

The inclusion of fan heat in coil sizing does not affect the coil output during the simulation (which has always included zone load, fan heat and outdoor air load). This change, the inclusion of fan heat in cooling coil sizing, only affects the calculation of coil size. You say the difference is only 2-20 W while the fan heat gain is 20-120 W. Can you check the zone loads reported in the eio and see if those still match. You could also use V9.0 and test how fan heat affects coil sizing by setting the fan's Design Pressure Rise to near 0 and compare with what you have now.

FanPowerTot = (FanVolFlow * DeltaP) / TotEff
DesFanHeat = MotEff * FanPowerTot + (FanPowerTot - MotEff * FanPowerTot) * MotInAirFrac
PeakCoilLoad = rhoair * DesVolFlow * (CoilInEnth - CoilOutEnth) + DesFanHeat
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Asked: 2018-10-18 22:36:49 -0500

Seen: 195 times

Last updated: Oct 19 '18