Hi eQuesters!
Can anyone help me here?
I installed main heating coil as well as reheat coil with delta T=30.
Heating capacity and cfm is not defined so that they will be auto-sized.
And, I keep having this warning saying that the system "might have
insufficient heating capability."
I increased "Zone Entering Max Supply Temp", "Hot Deck Max Leaving Temp."
But, the problem stays.
How do I increase the heating capability?
Thank you !!
DE
Thank you John,
But isn't airflow supposed to be auto-sized if not specified?
I intentionally leave the flowrate blank to let the program calculate the
cfm that serves load the best.
Should still I specifiy cfm?
DE
2011/7/23 John Aulbach
Hi DE,
If you look around at all the defaults you will probably find that somewhere
eQUEST is defaulting to 0.5 cfm/sf for your supply air. This is often
insufficient to meet your heating/cooling requirements. Things I have done
in the past to fix this is to use the same cfm/sf as the proposed building
uses, or look in the little ASHRAE Pocket Guide for what they recommend for
your building type. These two numbers will likely be similar
Carol.
Thank you Carol!
I modified "Min Design Flow(cfm/ft2) .
However, "insufficient heating" warning is keep showing.
Only thing seems to work to solve this problem is to increase heating
capacity is Reheat delta T.
(Its system is VAV with Reheat).
What I can't understand the most is that specifying heating capacity of main
heating coil doesn't
affect the heating capacity anyhow.
Any thoughts on this anyone???
Thank you!
DE
2011/7/25 Carol Gardner
I am not clear what this warning is saying as the wording is "MIGHT" have insufficient heating capability.? I too am getting this warning, but I have very little unmet heating hours. Increasing the cfm/sq.ft only increases total energy use but does not get rid of the warning.? It seems to me it may be a software issue rather than a design issue?
Did you try increasing the heating capacity of the central heating
coil or is is self-sizing. Are there under heated hours in the zones?
You note the warning is that the "system" may have insufficient
heating capacity. That doesn't sound like a zone problem so reheat
delta-t and zone entering max supply T likely are not the
problem. Hot Deck Max Leaving Temp. only applies to dual duct or
multi-zone systems (systems with 2 "decks"), not to single duct
systems like VAVS.
Chris Jones
By chance, does the building have a significant amount of glass at the
exterior in a climate where heating is required at some point during the
year? I have seen this warning persist in energy models of buildings
where the envelope load is unsatisfied due to lack of baseboard heat.
This is a design issue, though, and should probably be brought up to the
system designer instead of tweaked in the model until it goes away.
Cost and aesthetics are often used as reasons to eliminate baseboard
heat, whereas the energy model and some basic ASHRAE 55 calcs may show
that to be a bad choice (or at least give the energy modeler and the
system designer a CYA when the occupants start complaining).
Just a thought...
Jeremy R. Poling, PE, LEED AP+BDC
Hi Jeremy,
Yes there are a few areas with significant glazing, although the majority of the areas have relatively small glazing areas. The building is located near Toronto, so yes heating is required in winter. For one zone, the perimeter heating consists of radiant panels. Almost all rooms within this zone show this warning.?
The 2nd zone is a VAV system that does not have any reheat or baseboards, so I would expect this warning to pop up.?
My question still is should this not show up as unmet heating hours in the SV-R report if there is a heating problem?? Both zones have almost zero unmet heating hours.?
Thanks.
The last time this warning showed up for me in a zone with perimeter heating, it was due to the capacity of the perimeter heating component of the system, not the main system coils. Check the effect of increasing the capacity of the perimeter radiant panels and whether that removes the warning.
If I had to guess, the reason it would not show up as an unmet load hour in the SS-R report is that unmet load hours in that report are based on zone air temperature compared to the thermostat throttling-range. This warning seems to be discussing system capacity and my assumption has been that it results as a comparison of system size from the HVAC module of DOE2.2 to loads calculated by the LOADS module of DOE2.2. The space temperature may be within the throttling-range for all hours of the day while the capacity of the perimeter baseboard is less than the peak load due to the glazing. The zone air temperature is going to be a function of all components of energy transfer in the space (convection, conduction, and radiation) while the perimeter heating system is primarily intended to address the radiation component.
Someone at Hirsch would know specifically what generates this flag, but my experience has been that fixing the capacity of the perimeter heating component resolves this particular warning.
Jeremy R. Poling, PE, LEED AP+BDC
This raises another interesting question for me, if anyone can help:
If I wanted an hourly report showing me the hourly load due to the windows in the space, what variables would I need to tick on in an hourly report block to come up with the same number reported on the design day and hour in the LS-B report? I?ve looked at the intuitive ones and can?t come up with the load reported in the LS-B report.
That might be a useful way of identifying where/when the problem identified in this warning occurs.
Jeremy R. Poling, PE, LEED AP+BDC