Tim,
It sounds like the heating system is fighting the cooling system off and on (but moreso during your HDD's resulting in underheated hours). This can happen for a number of reasons. It could have to do with either exhaust fan settings to the zone or schedules that are at odds with each other (or both).
We call it the "yoyo" effect (or at least I do).
How to approach this depends on how you are modeling OSA, whether or not you re modeling exhaust fans in the space and what other factors apply (HW coils, RH coils, etc).
I would also go back and check your reports because they always give away the culprit in instances like this. Look for excessive heating and/or cooling loads in your zones.
The LS-A reports would be useful because the peak load summaries are zone-specific.
The zone air-side system will do it's best to maintain setpoint given the parameters you've specified. If you try to input more heat by manual methods, the system will still try to cool the space more at the same time to maintain setpoint- resulting in even more competition between the heating/cooling sides of the system along with a lot more energy usage than you are intending.
However, this also hints that the cause of the problem is elsewhere. Like Nick once told me - this is probably one of those cases where it's not an issue of "not enough heat" and more of a problem with too much heat AND too much cooling.
In the past, I've seen that checking OSA coming into the zone is useful along with ensuring any exhaust fans are being modeled with a schedule so that OSA coming in on the back-end doesn't ever exceed intended design specs.
Too much OSA isn't necessarily an issue that gives itself up right away in equest until the OSA temp gets to a point that your heating or cooling capacity isn't enough to heat or cool the space readily. And if this is the case, your exhaust fans will always tie in to the equation somehow (if modeled).
Hope this helps.
Chris Baker
CCI Alliance of Companies
Fort Wainwright, Alaska
907-356-1681 (x105) office
907-750-4922 cell
