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controlling a two zone house with VAV and Unitary system

asked 2022-04-03 14:41:59 -0500

Melina's avatar

updated 2022-04-04 09:53:32 -0500

Hello. I have a two-storey residential building, and because of different occupancy, I want to have two thermal zones: first floor and second floor. To do so, I have defined two zones, and each has an Airterminal: Single duct:VAV: no reheat. Also, I have defined an AirloopHVAc:Unitary system, and I'm not sure whether this is needed or not. From the examples that exist in EP version 9.5.0, I realized that I should define an AirloopHVAc: Unitary system. Still, I'm not exactly sure that this unitary system is which part of the system and even this is necessary or not, But I made sure to give the inlet and outlet node of this system correctly with the help of examples in version 9.5.0. I'm following is related to a commercial (office) building and is about 2000 m^2, but mine is a 150 m^2 house, so I do not want to copy and paste the HVAC system blindly from the example. My problem is that the example (5Zone_Unitary_VSDesuperheater) has defined a return zone and a return plenum, but I don't think this is a good idea for a house so I have not defined this part. Without an airloopHVAC: return plenum, my 2-zone building model works (I mean, there is no error after simulation). The tables show that there is HVAC heating and cooling energy consumption, and the numbers are reasonable and close to what I have from my previous simulations for this house (but as a single zone). The problem is that when I open the variable file, the temperature of both zones shows that these zones are not controlled at all. The temperature reaches less than 10C, but the set point for even unoccupied hours is not 10C (is 22C). This is obvious that the energy is wasted, but I'm not sure why this is happening? Is this because I have not defined the return plenum and return path, and I only have the supply path? there is not even one day that I can see that the temperature is being controlled! Can you help me and say what can be the source of the problem? Because EP doesn't give me any errors (and warnings are not related) I have no idea what should I do. I have to mention that most of the time the runtime fraction for the heating coil is 1 and the dampers are nearly fully open and my city is heating dominant.

Also, from the comments on this website (unmet hours) I realized that when I define the AirloopHVAc:Unitary system and I choose the control type to be "SETPOINT", I have to define some setpoint manager and honestly I did a copy and paste from the example file (5Zone_Unitary_VSDesuperheater) that I mentioned and I have no idea why I have to do this.

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answered 2022-04-04 07:18:56 -0500

Yes you do need the AirloopHVAC:UnitarySystem object since this is the HVAC unit that has the coils and fan. If you are controlling using SetPoint then you will need SetpointManagers to control operation. You also need to use constant fan operating mode. Use SetpointManager:SingleZone:Cooling (Tstat in 1 zone) or SetpointManager:MultiZone:Cooling:Average (Tstat in all zones) and similar for heating. If your fan is draw through then you will also need SetpointManager:MixedAir to adjust the set point for each coil. When you use more than 1 set point manager AND you have a draw through fan, keep the cooling and heating set points separate. Set the cooling set point at the air loop outlet node and heating set point at the air loop inlet node. Then use the mixed air managers to reference each of those nodes and write to the coil outlet nodes. If you are NOT using a draw through fan you can write directly to the coil outlet nodes (since you don't have to adjust for fan heat).

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Thank you for your answer and sorry for my late follow-up. I have a blow-through supply fan and I did whatever you said but again I have the same problem, my zones are not controlled. This time energy is not wasted since I can see the cooling energy and heating energy are both zero and the coils runtime faction is zero too. For example, the room temperature is 10C and the setpoint is 22C in winter but the system cannot (or does not know that it should work!) be turned on.

Melina's avatar Melina  ( 2022-05-30 10:10:50 -0500 )edit

I made a new IDF, this time very simple. I used "HVAC template:packaged VAV" but the problem here is that for choosing the cooling coil there is only a two-speed cooling coil option and I have to use single-speed for my research. I've reached a dead-end! I can use your help if you have any recommendations for me! Thank you so much for your time.

Melina's avatar Melina  ( 2022-05-30 10:13:29 -0500 )edit

Also, I'm using zone capacitance multiplier. I saw in my previous simulations that this parameter can even cause errors if we choose the wrong number. Or it can change the runtime fraction of the coils. Do you think that this parameter can be the source of my problem? (my problem is that the zones are not controlled, although the system does not give me any errors). I tried every integer between 15 and 30 for the zone capacitance multiplier for each zone. (I have 2 zones).

Melina's avatar Melina  ( 2022-05-30 10:18:10 -0500 )edit

Are there any errors in the err file that would help identify a problem?

rraustad's avatar rraustad  ( 2022-05-31 06:07:12 -0500 )edit

Unfortunately, it doesn't give me any error or related warning.

Melina's avatar Melina  ( 2022-05-31 09:39:53 -0500 )edit

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Asked: 2022-04-03 14:41:59 -0500

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Last updated: Apr 04 '22