Zone cross mixing in energyplus
I have an inquiry on setting up ZoneCrossMixing object.
I simulated 2 cases (cross mixing case and no cross mixing case) by changing the relation of inter-zone heat & mass transfer and compared. However, there was no difference in the temperature of each zone in the non-air-conditioned time zone in each case. So I really appreciate if you could have advices or comments on this matter.
The description of how I set the ZoneCrossMixing object in the cross mixing case is as follows. If you see the object of PneandPn((perimeter North East zone & perimeter North zone), I set the ZoneCrossMixing object as follows, Zone Pne and Zone Pn to be source and receiving zone. The reason I set is that crossmixing occurs only in the case of “the temperature of source Zone－the one of Receiving Zone＞＝ ΔT (default=zero )”. I believe that it should occur in the case of the “temperature of Receiving Zone－the one of source Zone＞＝ ΔT (default=zero)”. So I set this way to all the inter-zone.
And I set the design flow to an amount equivalent to 0.5 ventilation per hour in a smaller zone. (Pne floor area: 40.96m2, Pn floor area: 245.76m2, Ceiling Height: 2.6m) In the idf editor, design flow rate unit is m3/s, so I used this unit. However, I suspect that the correct unit is m3/min. (Because after I changed the unit, I got the result seemed to be correct.)
ZoneCrossMixing,
1F:PneAndPn, !- Name
1F:Pne, !- Zone Name
On, !- Schedule Name
Flow/Zone, !- Design Flow Rate Calculation Method
0.016, !- Design Flow Rate {m3/s}
, !- Flow Rate per Zone Floor Area {m3/s-m2}
, !- Flow Rate per Person {m3/s-person}
, !- Air Changes per Hour {1/hr}
1F:Pn; !- Source Zone Name
ZoneCrossMixing,
1F:PnAndPne, !- Name
1F:Pn, !- Zone Name
On, !- Schedule Name
Flow/Zone, !- Design Flow Rate Calculation Method
0.016, !- Design Flow Rate {m3/s}
, !- Flow Rate per Zone Floor Area {m3/s-m2}
, !- Flow Rate per Person {m3/s-person}
, !- Air Changes per Hour {1/hr}
1F:Pne; !- Source Zone Name
I think that my way of setting for this ZoneCrossMixing object must be wrong since there are no big difference between the results of the cases.
Have you investigated if there are other things happening in the zone that could minimize the impact of the cross mixing? Such as high infiltration rate, high terminal airflow rate, etc. Is the delta between the zone temps big enough to see the impact? Also are you looking at hourly time series results?
I don't have the answer but I have a quick question. How do you determine / calculate the design flow rate in this case ? The 0,016 m3/s, where does it come from ? It's always though and unclear for me to calculate the design flow rate for the zone croos mixing object.
@David Goldwasser Thank you for asking for more information. In this case, the infiltration rate is set to zero and I check each zones temperature when the air conditioners are off (so there is no terminal air flow). The max delta between the zone temps is about 1~2℃. I'm checking at hourly time series results.
@Alexis In this case, Pne zone floor area is smaller than that of Pn zone, so I calculate design flow rate based on Pne zone floor area. the air volume of 0.5 ventilation per hour is 40.962.60.5 [m3/hr]=0.015[m3/s] (sorry, correct value is 0.015 not 0.016.) However, I'm not sure if this zone cross mixing setting is correct.