RE: [EnergyPlus_Support] Re: Why T becomes so low

Hi, Xing

Because you are using set point manager on the AHU system for cooling, the zone temperature is not directly controlled by the zone thermostat.

You are using the reheat heater for Winter heating, this is controlled directly by the zone thermostat.

I think you need to have two set points on the Controller:MixedAir for cooling control, one on the mixedAir node and one on the outlet CW coil node. The fan may need to be variable speed, as this is now working like a VAV system, but without the VAV dampers in the zones.

The setpoint temperature may not be those in your schedule, this is where I am trying to trace. It could be the temperature of the cooling coil. In general, the cooling set point must be be set too low, and to a value just below the thermostate cooling setpoint. Because you do not have a damper control, the zone theremostat do not have a damper to adjust to control te zone temperature.

Display the system node temperature values, and that may lead you to the point which causing the low temperature. I am doing this at the moment, and will let you know what I find..

Dr. Li

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: xing.shi.2006@xxxxxxxxx
Date: Thu, 8 Sep 2011 23:33:58 +0000
Subject: [EnergyPlus_Support] Re: Why T becomes so low

Dr. Li,

Thank you again for your detailed reply!

The interesting thing is that the winter zone T was maintained well as we hoped (setpoint 20 degree C during occupied hours). In summer, the zone T (from 1-k to 5-k) is kept too low. The setpoint is 26 degree C but the zone T goes down to 20.

Based on the above observation and checking the SVG, it appeared that 1-k to 5-k zones are connected with the HVAC. Otherwise, what is adjusting the zone T?

We will try to understand the equipment grouping advice you gave us. If you changed our IDF and got what you consider correct, would you please kindly email it to shixing_seu@xxxxxxx? For whatever reason, I cannot download attachments from this website.

Many thanks!

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@...> wrote:
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> A few more points that I have observed.============Compact schedules:For: WeekendsAndAllOtherDays includes the DesignDays. Therefore my DesignDay only simulation do not see the system running. Normally, the DesignDay should be with the weekdays, unless the load is higher at the weekends. When the system is not available, the temperature setting has no effect.===============ZoneHVAC:EquipmentConnections, 1-K, !- Zone Name Zone1Equipment, !- Zone Conditioning Equipment List Name Zone1Inlets, !- Zone Air Inlet Node or NodeList Name , !- Zone Air Exhaust Node or NodeList Name Zone 1 Node, !- Zone Air Node Name Zone 1 Outlet Node; !- Zone Return Air Node Name This is where you changed the zond name. Normally, Zone1 should remain as 1-K.==========================##def ZoneHVAC_EqCn [ ZoneNM ]ZoneHVAC:EquipmentConnections, ZoneNM, !- Zone Name ZoneNM EquipmentList, !- Zone Conditioning Equipment List Name ZoneNM Air Inlet Node, !- Zone Air Inlet Node or NodeList Name , !- Zone Air Exhaust Node or NodeList Name ZoneNM Air Node, !- Zone Air Node Name ZoneNM Air Outlet Node; !- Zone Return Air Node Name##enddef=========================ZoneHVAC_EqCn [ 1-K ]ZoneHVAC_EqCn [ 2-k ]ZoneHVAC_EqCn [ 3-K ]ZoneHVAC_EqCn [ 4-K ]ZoneHVAC_EqCn [ 5-K ] Typing the above five lines in the .imf file will expended to the five objects in the .empIDF file. The people, electric, equipment list, zone equipment, etc. can all be included in the above macro list definition.============AirLoopHVAC, Typical Terminal Reheat 1, !- Name Reheat System 1 Controllers, !- Controller List Name Reheat System 1 Avail List, !- Availability Manager List Name autosize, !- Design Supply Air Flow Rate {m3/s} Air Loop Branches, !- Branch List Name , !- Connector List Name Air Loop Inlet Node, !- Supply Side Inlet Node Name Return Air Mixer Outlet, !- Demand Side Outlet Node Name Zone Equipment Inlet Node, !- Demand Side Inlet Node Names Air Loop Outlet Node; !- Supply Side Outlet Node Names
> You are calling this air loop as a reheat terminal. Actually it is a system AHU [AHY1 system].The air loop branches list points to the air loop main branch which includes the OA mixer box, cooling coil and the fan. All the components in the macro should have the AHU1 as the prefix. =======I have not found the set point temperature for the AHU. Because you are using setpoint control for the coil, the zone thermostat is not used directly. I shall try to re group your file to trace the air loop controllers and the cooling coil controller, and the controller MixedAir. Dr. Li
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> From: xing.shi.2006@...
> Date: Wed, 7 Sep 2011 23:58:24 +0000
> Subject: [EnergyPlus_Support] Re: Why T becomes so low
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> Dr. Li, thanks!
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> We checked the SVG diagram and it seemed to be correct. In our configuration, only 5 big zones (from 1-k to 5-k) are conditioned spaces.
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> The shading of the basement is a minor thing because the basement wall has some little spaces outside that are digged down to provide natural lighting.
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> By the way, for some reason, I cannot download the error file you uploaded.
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> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@> wrote:
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> > Hi, HanSin I had simulated your IDF and had a quick look at the result. The error file is attached. The simulation configuration is not correct. The five fan coils in the air loop are not connected to any zones. Zone 1 to zone 5 do not exist in you IDF. You have infiltration in all zones. The zone temperature is simply flowing the outside air temperature and regulated by the ground temperature. There is no zone heating or cooling load. Zone -1-T seems to in the basement. There are errors on shading. If -1-T is a basement, then all the shading on the windows are very strange arrangement. I cannot tell exactly, because your z in the zone origin is 3.5 and the z in the floor is -7. I always use one origin for the building input.
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> > Dr. Li
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> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
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> > From: xing.shi.2006@
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> > Date: Wed, 7 Sep 2011 18:35:36 +0800
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> > Subject: [EnergyPlus_Support] Why T becomes so low
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> > Attached is our IDF file. It is a 5-story building with two chillers for cooling and electric heating. The srange thing is that the simulation shows that the zone T is well controlled as the schedule defines in winter (20 degree C). However, in summer the schedule wants to maintain the zone T at 26 degree C but the output shows that the T overshoots to 20 degree C.
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> > We replaced the HVAC system with IdealSystem and the zone T is well controlled. I guess this means that the schedule has no error. We have been working on this problem for several days and are really puzzled.
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> > Please help. Thanks! XS
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