[Equest-users] Electric duct heaters

Thu Apr 28 13:51:53 PDT 2016

Nicholas,

Many thanks for these tips. They were very helpful and I was able to get rid of unmet hours in the dummy zones.

To answer the second part of your comments, the remaining systems with heating unmet hours in the cellar and first floor are modeled per the actual design. They are served by the same heat pumps despite their different load profiles. We are also providing electric heaters in zones served by heat pumps to address perimeter loads. The issue here would be to be able to model the supplemental heating from these heaters at the ZONE level (and still model the HP heating capacity at the SYSTEM level). I do not think it is possible in eQuest.

Again, thank you for your help.

Regards,

Manuela

From: Nicholas.Caton at schneider-electric.com [mailto:Nicholas.Caton at schneider-electric.com]
Sent: Wednesday, April 27, 2016 2:12 PM
To: Manuela Mengue
Cc: equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Electric duct heaters

Hi Manuela,

Following is a plot of OADB (red) vs. interior space temperature (blue) for the C-DUMMY zone, for the first ~500 hours of the simulation:

[cid:image002.png at 01D1A155.F2D34840]

Note a few things:

-          Every hour your space temperature is bouncing like a pinball around your setpoint (40F), oftentimes beyond the throttling range (registering an unmet hour).

-          While the hourly need for heating remains constant (OA remains below 40F), the "pendulum" swing hour by hour gradually lessens over time.

-          When OA crosses the setpoint line (>40F), the resulting swing after it drops again can be either mitigated or exacerbated depending on whether the system was trying to heat in that hour.  Kinda like jumping on a trampoline out of sync with a friend - depending on timing, you may lose all momentum or you may rocket into the sky!

Now let's look at the "whole year" picture for the same plot:

-          You can more clearly see the above behavior repeating through the winter months

-          The pendulum swinging is actually worst in the spring/autumn (when OA more frequently crosses the 40F line), but the general hourly behavior (hot/cold/hot/cold) doesn't really ever go away...

[cid:image003.png at 01D1A155.F2D34840]

These behaviors led me to guess (correctly) that you have little (zero) thermal mass in your dummy zones.  Freezing air comes in one hour so the system turns on, the space gets overheated next hour the next so system turns off, rinse and repeat.

I tried making this tracked dummy zone bigger (100ft x 100ft), adding a single interior wall to the bottom (of type INTERNAL so no thermal connections elsewhere in your model), and assigning a library LAYERS construction (any of the ASHRAE Concrete walls should do) to effectively give it some thermal mass to store heat hour by hour.  The result is zero unmet hours (for that zone) and this "bouncing" behavior goes away:

[cid:image004.png at 01D1A155.F2D34840]

After fixing the flailing dummy zone temps by adding thermal mass, you may wish to re-evaluate whether the heatpumps are receiving tempered OA.

I'm not aware of a particularly simple/direct way to do so short of crunching a bunch of custom hourly SYSTEM and ZONE outputs to work it backwards from the coil leaving temperature (any tips from the crowd that uses dummy zone workarounds for DOAS more regularly?)... however if I more simply set you're the above "DUCT" system to SUM & remove the associated OA-FROM-SYSTEM inputs (effectively pushing all required OA conditioning back onto the "receiving" heatpump systems - whose heating capacity inputs are fixed/specified), I observe the associated spaces shift from "many" annual unmet heating hours to "many more..." This suggests (A) the contributions of OA-FROM-SYSTEM tempering exist and are at least mitigating the situation, and (B) you probably have issues beyond OA temperatures to deal with.

A few other things caught my eye along the way:

*         Like the dummy zone discussed above, ALL of your assigned envelope constructions & floors are "massless" (defined with the U-value specification method in lieu of layers).  I expect if we plot more zone temperatures we would find more pinball behavior!  Switching to constructions with thermal mass is probably going to help reduce unmet hours altogether.

*         I notice substantial unmet hours outside of the dummy zones, and that you have chosen to group zones with likely dissimilar load profiles under PVVT systems - bear in mind the typical relationship for the control zone vs. the "slave" zones when evaluating whether those unmet hours are meaningful... you might want to re-evaluate your system quantities and/or whether a few thermostat schedules should be removed where they don't exist in the actual design.

I hope that helps you and others!

~Nick

------------------------------------------------------------------------------------------------------------------------------
Nick Caton, P.E.
  Senior Energy Engineer
  Energy and Sustainability Services
  North America Operations
  Schneider Electric

D  913.564.6361
M  785.410.3317
E  nicholas.caton at schneider-electric.com<mailto:nicholas.caton at schneider-electric.com>
F  913.564.6380

15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219
United States

[cid:image001.png at 01D189AB.58634A10]

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Manuela Mengue via Equest-users
Sent: Wednesday, April 27, 2016 7:51 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Electric duct heaters

Dear All,

Water source heat pumps are serving spaces in the cellar and first floor that are of concern for this model. Please review the eQuest energy model attached. I am trying to find the appropriate way to model two electric duct heaters and outside air fans on the cellar & first floors mainly utilized  to provide outside air to the WSHP units on these floors. The electric duct heaters heat the outside air from 0F to 40F (cellar) or 60F (first floor).  The temperature of entering outside air should be 40F for units "C EXERCISE ROOM SYS", "C AC SYS" AND "C SCREEN ROOM SYS" on cellar floor, and 60F for units "1 LOUNGE", "1 LOBBY SYS" and "1 CORR BIKE MAIL SYS" on first floor. I created two heating and ventilation systems "C DUCT HEATER" and "1 DUCT HEATER", and fixed the heating set point temperatures to 40F and 60F respectively. I also created and assigned dummy zones with no internal gains to these systems. After simulation, I am getting extremely high heating unmet hours for the dummy zones, plus the zones served by the above systems do not seem to receive outside air at the appropriate temperature. I am wondering if some inputs in my model are incorrect. If possible, can anyone please indicate how this design strategy should be modeled and the resulting issues addressed ?

Thank you,

Manuela

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
______________________________________________________________________
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20160428/55ff94dd/attachment-0005.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.png
Type: image/png
Size: 87681 bytes
Desc: image002.png
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20160428/55ff94dd/attachment-0020.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image003.png
Type: image/png
Size: 131832 bytes
Desc: image003.png
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20160428/55ff94dd/attachment-0021.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image004.png
Type: image/png
Size: 94626 bytes
Desc: image004.png
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20160428/55ff94dd/attachment-0022.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image005.png
Type: image/png
Size: 7893 bytes
Desc: image005.png
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20160428/55ff94dd/attachment-0023.png>