Heat not working!

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All,

I'm modeling a building and for some reason I can't get the heat to turn on.
The building is a VRF system - we are tricking a heat pump system into a VRF
system per BSUG directions (attached).

I've attached the model file. Can someone take a look and see what I did
wrong?

Thanks,

Terrence W. Budd, P.E., CPD, LEED AP

Terry Budd's picture
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Joined: 2011-09-30
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Good morning Terry-

One very common problem that causes unmet load hours during heating is not using a minimum OA schedule to eliminate OA during unoccupied times.

Also, you should check your fan and heat temperature schedules for consistency; i.e. for each hour that has an occupied temperature setting, the fan must be set to "1".

In addition, if using night set-back, you should also use an optimum start for 2-3 hours before occupancy to bring the temperature back up to the occupied setting in smaller increments. Using optimum start affects both the temperature schedule and the fan schedule. And, the min OA schedule should have a "0" during any optimum start hours so that no outside air is brought in while bringing the temperature back up to occupied settings. Keep in mind that a zero in the min OA schedule will disable the economizer. If economizer use is desired, the unoccupied hours should be set to 0.0001 to limit the OA when not desired but still allow the economizer if conditions are favorable.

Hope this helps.

Have a nice day.

Sheila Sagerer

Sheila's picture
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Joined: 2011-09-30
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Terry,

I took a look at your model file. Here's a few things I notice even before
I could look at your heating systems.

1. You file takes a REALLY long time to open--from observation you have
way too many zones (think "thermal zones", not spaces.) There is no need in
a simulation model to simulate/zone each space individually. You should
combine thermal zones that are similar in thermal characteristics (i.e. same
exterior exposure, same space type occupancy, etc.) It makes the model &
variables too complicated to manage when you are giving attention to very
space in your building design. For your sake, and anyone reviewing your
model you should go back to the wizard and simplify your zoning patterns.
This will help to reduce the number of inputs that you have to pay attention
too as well.
2. In your 3-d model view you have some spaces on the second level that
do not have exterior wall constructions. You may or may not have noticed
the spaces with "white" walls or effectively no ext. walls. Your sim calcs
are not accounting for thermal & energy losses across these spaces, so your
loads will be underestimated in the program and thus your overall energy
consumption will be under-estimated. This issue happens when you do not
line your zone outlines up with your building footprint ext wall outlines.
To fix the probelm you will need to go back to wizard mode and re-enter your
zones for those spaces. (I can talk you through this if you need assistance
with it.)
3. When I run the simulation you have results (energy consumption) for
Misc. Equipm under gas consumption. What type of equipment are you
simulating for misc. equip. gas consumption? Seems not right to me, but I
don't know the details of your project...school & classrooms I assume.
4. Looking at your BEPU/BEPS reports you have 89% unmet loads. Looking
at the SS-F reports you have issues of underheating & undercooling, which is
signifying that conditioned air is not getting to where it needs to
go---what's blocking it? ...I'm trying lots of things--(lesson: don't be
afraid to do experiments and test your inputs.
5. For your undercooling try removing (undefine) your cooling
availability schedule that is defined in the systems-cooling control tab.
6. For your underheating, add baseboards at both the system level and
zone levels, specify thermostatic (not outdoor air) and some amount of
capacity at the zone level (like -50000.)
7. For any other unmet hours you will need to experiment with your inputs
primarily the schedules or controls inputs, this is likely where your unmet
conditions are steming from. Ask yourself what would contribute to cooling
not being met in the space and then investigate the different inputs that
might (or might not) affect the situation. This is where the engineering
analysis and scientist abilities come into play and can differentiate
between any old energy model and a good quality energy model. It is up to
you to best represent what your client is asking for.

Good luck with the rest of your model, come back and ask more questions when
you come upon them.

Pasha

Pasha Korber-Gonzalez's picture
Joined: 2011-09-30
Reputation: 600