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why my zone have heating load in summer?

asked 2018-08-02 15:24:06 -0500

taher.ahel gravatar image

updated 2018-08-02 16:10:41 -0500

I have a greenhouse zone that is controlled with an ZoneHVAC:EvaporativeCoolerUnit and ZoneHVAC:Baseboard:Convective:Water that coupled with hot water plant loop. the thermostat adjust the zone temperature between 16-18 deg C.

Sometimes baseboard sys and HW plant loop are on when There is cooling load , but EvaporativeCoolerUnit is always off when there is no cooling load. image description

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I mean why Baseboard sys work when EvaporativeCooler is on. For instance in summer we don't need Baseboard sys but it works.

taher.ahel gravatar imagetaher.ahel ( 2018-08-07 00:36:40 -0500 )edit

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answered 2018-08-08 09:40:17 -0500

updated 2018-08-14 09:45:41 -0500

From the data shown, it appears that the evaporative cooler is overcooling the space, and the baseboard heat is coming on to maintain the zone heating setpoint. In the ZoneHVAC:EquipmentList set the heating and cooling sequence numbers so that the baseboard heat is first (1) and the evaporative cooling is second (2). This way the baseboard will only run if there is a heating load, regardless of what the evap cooler does. You may want to review the evap cooler controls if the space gets too cold.

Additonal details

When ZoneHVAC:EvaporativeCoolerUnit control type is ZoneCoolingLoadOnOffCycling, the unit is fully on for a timestep any time there is a cooling load, no matter how small. This can lead to significant overcooling during offpeak times. Until better controls are implemented via #6707 use several smaller units with SequentialLoad operation in the ZoneHVAC:EquipmentList. This will stage the units sequentially as needed.

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I've checked any types of ZoneHVAC:EquipmentList sequences but it didn't work. I checked Evaporative cooler controller but I found nothing wrong.

taher.ahel gravatar imagetaher.ahel ( 2018-08-10 05:53:22 -0500 )edit

The evap cooler is overcooling the zone. Report at the "detailed" frequency and add output variable "Zone Evaporative Cooler Unit Sensible Cooling Rate". The evap cooler flow rate is set to 220 m3/s (466,153 cfm). That seems quite large. What weather are you using? Back to the evap cooler controls. As mentioned [here] the evap cooler "ZoneCoolingLoadOnOffCycling" control method runs for an entire timestep at full flow. Not very useful, especially at low part-load times. You could use variable speed instead, but the pump power stays at full.

MJWitte gravatar imageMJWitte ( 2018-08-10 14:31:26 -0500 )edit

Forgot the link above, see issue 6707. The only workaround I can think of is to use multiple smaller evap coolers, that should stage the operation so that the overshoot is smaller.

MJWitte gravatar imageMJWitte ( 2018-08-10 14:33:08 -0500 )edit

Thank you Mr Witte, I've utilized 2 EvaporativeCoolerUnit with 2 Fan:VariableVolume and the problem have been solved.

taher.ahel gravatar imagetaher.ahel ( 2018-08-13 10:28:48 -0500 )edit

but something wild!!!

My greenhouse has 18 fans that each fan provides 45 m3/min (12.2 m3/s, 1589 CFM) and totaly 18 fans can provide 220 m3/s. I've used 4 Parallel ZoneHVAC:EvaporativeCoolerUnit coupled with 4 Fan:ConstantVolume , But there were overcooling state and the resuilts were exactly similar to condition that I used 1 EvaporativeCoolerUnit. because of the fact that they works together at the same time and the load will be devided equally on them.

taher.ahel gravatar imagetaher.ahel ( 2018-08-13 10:32:34 -0500 )edit

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Asked: 2018-08-02 15:24:06 -0500

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Last updated: Aug 14