EnergyPlus: dual thermostat doesn't work, system working towards lower temp. all the year round

asked 2018-06-05 05:16:01 -0500

Allison Pan 611
71 ●1 ●1 ●7

updated 2018-08-25 18:21:28 -0500

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

Hi guys,

I got a hotel model (a FCU+PAU proposed model compared with LEED baseline) with dual thermalstat setpoint (22~24/25 generally) all the year round. Somehow the HVAC energy consumption is way higher than expectation. When I digging out the issue. It is found that some area are working towards the 22 degree C all the year round. For me it seems that the system overcools and then reheat but the setting are quite general that I have struggled for a while but just cannot find how to correct it. The Sensible Heat Gain Summary also shows something weird that 'HVAC Zone Eq & Other Sensible Air Cooling [kWh]' shows considerabily positive heat gain.

I have a attached the schedule setting and also sensinble heat gain summary. Can anybody help to have a look what is going wrong? many thanks!

Allison

Schedule:Compact,
Office Heating SP Sch,   !- Name
Temperature,             !- Schedule Type Limits Name
Through: 31 Dec,         !- Field 1
For: AllDays,            !- Field 2
Until: 06:00,            !- Field 3
-50,                     !- Field 4
Until: 07:00,            !- Field 5
14,                      !- Field 6
Until: 08:00,            !- Field 7
20,                      !- Field 8
Until: 19:00,            !- Field 9
22,                      !- Field 10
Until 20:00,             !- Field 11
20,                      !- Field 12
Until: 21:00,            !- Field 13
14,                      !- Field 14
Until: 24:00,            !- Field 15
-50;                     !- Field 16

Schedule:Compact,
Office Cooling SP Sch,   !- Name
Temperature,             !- Schedule Type Limits Name
Through: 31 Dec,         !- Field 1
For: AllDays,            !- Field 2
Until: 06:00,            !- Field 3
100,                     !- Field 4
Until: 07:00,            !- Field 5
26,                      !- Field 6
Until: 19:00,            !- Field 7
24,                      !- Field 8
Until: 24:00,            !- Field 9
100;                     !- Field 10

HVACTemplate:Thermostat,
Office_thermo,           !- Name
Office Heating SP Sch,   !- Heating Setpoint Schedule Name
,                        !- Constant Heating Setpoint {C}
Office Cooling SP Sch,   !- Cooling Setpoint Schedule Name
;                        !- Constant Cooling Setpoint {C}

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answered 2018-06-11 03:26:23 -0500

Allison Pan 611
71 ●1 ●1 ●7

After further compare the node supply temperature from DOAS and FCU. The reasons have been found. Turns out he PA/DOAS is oversized too much in MEP design that during summer time a huge amoung of cold air is supplied by DOAS which makes the indoor temperature lower then the lower limit of thermostat setpoint. The FCU hence has to heat up back. So the system is always struggling to heating to reach the lower temp. setpoint. So the model itself is working exactly as I told only problem with design.

One other thing I hope to get clarification is that I was told the PAU(DOAS) does not allow the heating setpoint to be higher than cooling setpoint as in energyplus they work in sequence. Setting higher heating setpoint will result in the air to be overheated first and then cooled back again. Is that ture? How can I resolve to avoid this problem ? (say to let the heating and cooling coils of PAU works indepentantly depends on terminal demand while not simutaneously even it is a four-pipe system)

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answered 2018-06-07 12:25:31 -0500

Viper
61 ●3

Are you sure in the Schedule:Compact object, the syntax Through: 31 Dec is legitimate?

In my idf file, it is always Through 12/31.

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hi I checked that in my model some shows throught 12/31 and some shows Through: 31 Dec. But after check hourly thermostat profile,seems generally works fine.