Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
eQUEST by default does not create a central heating coil in variable volume systems. The default assumption seems to be that the mixed air temperature will be sufficiently warm that all heating can be done by the VAV boxes and/or baseboards in the zones. However, this assumption does not apply to cold climates! As you have noted in your question, setting the "Hot Deck Max Leaving Temp" to 95F corrects the above error message by forcing eQUEST to add a central heating coil to the system to heat the supply air. If you look at the DOE-2 Dictionary you will see that this activates the keyword "HEAT-SET-T = 95".
If you are jacking up the baseboards and the reheat terminals to address the unmet heating hours, it is possible that the boiler is autosizing to a much higher capacity than is necessary. If the boiler is oversized, this could cause the seasonal heating efficiency to be low and the heating energy consumption to be exaggerated. I recommend that you set the "Hot Deck Max Leaving Temp" to 65ºF (or whatever your VAV system supply air reset temperature is in heating mode), and reset the capacity of the VAV reheat boxes and baseboards to default to autosize their heating capacity. Run the model and look at the .SIM file to see what is happening with the unmet load hours and the boiler sizing. The SS-K report will show the unmet hours by zone which should allow you to figure out which zones are causing problems. I recommend using baseboards set to thermostatic control. The PV-A and PS-C reports will tell you what is happening with the boiler sizing and utilization. These reports should give you enough information to manually size the boiler near the peak heating load. Hopefully this will address the unexpectedly high heating energy.
