Dear All,
My model is located in Mexico and three zones are equipped with VFD. So I
selected Pkgd Var Vol + Heat pump for these three zones and set the system
up by the design cooling and heating capabilities. Currently, the SS-R
shows 4380 under heated hours for each of the zones. And no space heat is
provided for any of the zones. Does anyone know the possible reasons for
this phenomenon?
I've done several solutions by searching:
- Increased Throttling Range
- Night Cycle Control --> Set to "Cycle on Any"
- Fan Control and Placement - Set to" Hourly Report Schedule"
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Thank you!
Jing
Jing;
First thing that jumps out at me is that there is no Heating Discharge Air Tempertaures or Reheat Temperatures set on the System>Heating Tab (last image you shared). For a VAV System I?d expect these values to be something like: Zone Max Temp: 90F Hot Deck Max Leaving Temperature 60F and Reheat Delta T: 35F.
Thanks,
DARIC R ADAIR PE, CEM, BEMP
Mechanical Engineer, Energy Analyst
Henderson Engineers
daric.adair at hendersonengineers.com
Licensed in KS
Jing,
It's been a while but I'm remembering back to my days using VisualDOE. You
might want to check how your thermostat is defined. To get heating to
simulate properly with a VAV system, the thermostat needs to be defined as
reverse acting. Take a look at this.
My best,
Mike Busman CEM
Retired Senior Energy Engineer
On Tue, Nov 13, 2018 at 1:32 PM Daric Adair via Equest-users <
Hi Daric,
Thanks for your quick response. I updated the heating tab with
your suggested temperature setting, but still has no space heat provided
and the same unmet heat hours. This system does not include any reheat coil
nor zone level VAV box. Only rooftop units with VFD. The cooling parts have
no unmet cool hours, but the heating parts are very odd.
Jing
On Tue, Nov 13, 2018 at 3:32 PM Daric Adair <
Michael,
Thanks for your response. I think you are correct that the Thermostat type
should be Reverse Action for VAV. I changed the thermostat type to
"Reverse Action" accordingly, but the space heat is still ZERO.
Jing
reheat You need a reheat coil for VAV !!!
Sent from Yahoo Mail on Android
On Tue, Nov 13, 2018 at 1:59 PM, Jing Hong via Equest-users wrote: _______________________________________________
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Jing;
John Aulbach is right on.
This may be an issue of modeling vs reality then. With a ?Packaged VAV? eQuest believes that there are VAV boxes downstream, so it will put out cold air to provide cooling and depend on the VAV Boxes to reheat and prevent over-cooling.
You may want to try a PVVVT system since that requires specifying a control zone, and that will allow the System to provide hot/cold air based on the control zone. The other 2 zones will be slaved along to them, providing either heating or cooling ? whatever the control zone dictates it needs. But it doesn?t require VAV boxes (as your system doesn?t have them)
The Thermostat Control should not enable/disable/prevent heat. A Single Max VAV system uses ?Proportional? and a Dual Max VAV System needs ?Reverse Acting?. Proportional just allows eQuest to provide CFM up to the max durring cooling and turn down to the minimim ratio as coolng load ecrease and then jump to the minimum heating ratio (if a dual min box. If single min box, then the min ratio and min-heatig-ratio will be the same). Reverse acting just means that as the heating load increases, the box can allow more airflow up to the Heating Maximum Airflow (making it a dual max box.)
The main issue may be the incorrect system type in eQuest vs the actual system type that is attempting to be modeled.
Thanks,
DARIC R ADAIR PE, CEM, BEMP
Mechanical Engineer, Energy Analyst
Henderson Engineers
daric.adair at hendersonengineers.com
Licensed in KS
Thank you John. It is a proposed model based on an existing design. So my
model is basically showing what they have. The part confused me the most
was that maybe the unmet hours are due to being lack of reheat coil, but
how could the heating is 0 throughout all the zones. Is that possible?
Jing
Thank you Daric and John!!!!!
Choosing Package VAV is the trigger for the error. I changed it to PVVVT
and it worked! With minimal unmet hours. You guys saved my life. LOL. I
have tried everything I googled out these days.
Thank you!!!
Jing
On Tue, Nov 13, 2018 at 4:06 PM Daric Adair <
We expect dinner...
Sent from Yahoo Mail on Android
On Tue, Nov 13, 2018 at 2:21 PM, Jing Hong wrote: Thank you Daric and John!!!!!Choosing Package VAV is the trigger for the error. I changed it to PVVVT and it worked! With?minimal?unmet hours. You guys saved my life. LOL. I have tried everything?I googled out these days.?
Thank you!!!
Jing
Jing;
?
John Aulbach is right on.
This may be an issue of modeling vs reality then. With a ?Packaged VAV? eQuest believes that there are VAV boxes downstream, so it will put out cold air to provide cooling and depend on the VAV Boxes to reheat and prevent over-cooling.
?
You may want to try a PVVVT system since that requires specifying a control zone, and that will allow the System to provide hot/cold air based on the control zone. The other 2 zones will be slaved along to them, providing either heating or cooling ? whatever the control zone dictates it needs. But it doesn?t require VAV boxes (as your system doesn?t have them)
?
The Thermostat Control should not enable/disable/prevent heat. A Single Max VAV system uses ?Proportional? and a Dual Max VAV System needs ?Reverse Acting?. Proportional just allows eQuest to provide CFM up to the max durring cooling and turn down to the minimim ratio as coolng load ecrease and then jump to the minimum heating ratio (if a dual min box. If single min box, then the min ratio and min-heatig-ratio will be the same). Reverse acting just means that as the heating load increases, the box can allow more airflow up to the Heating Maximum Airflow (making it a dual max box.)
?
The main issue may be the incorrect system type in eQuest vs the actual system type that is attempting to be modeled.
?
?
?
Thanks,
DARIC R ADAIR PE, CEM, BEMP
Mechanical Engineer, Energy Analyst
Henderson Engineers
daric.adair at hendersonengineers.com
Licensed in KS
?