Crazy High Unmet Heating Hours on ASHRAE 90.1 Baseline Model

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Good afternoon everyone!

I am working through the process of creating an ASHRAE 90.1-Appendix G baseline model and cannot understand where I've gone wrong in the design. I have done a number of energy audits using eQuest but have never been through the LEED process and thus this is my first attempt at dealing with 90.1 directly. Any help you may offer would be much appreciated and I am more than happy to compensate any time spent.

The building is a System Type 7 - VAV with Reheat - and my cooling hours are 0. However, I can't seem to get my VAV terminal units to provide enough heat at any time during the year. When I allow eQUEST to size the capacities on their own, not enough heat is added and temperatures throughout the winter and in all zones remain below 60F. But when I specify a Maximum Heating Rate at the Zone Terminal the addition rate doesn't change! I've tired increasing the throttling range, which had some effect. The only thing that had a significant effect on the unmet heating hours was increasing the Heating Design Temperature for each Zone. But this also had the effect of dramatically increasing the cooling unmet hours! Finally, and most confoundingly, my heating energy consumption in the winter is significant! Where is it all going?? I am at a total loss.

I hope I was clear in articulating my issue and again appreciate your assistance.

Dana M. Savage :: Mechanical Engineer
CONTACT :: DSavage at :: C: 301.717.0003
ADDRESS :: 20251 Century Blvd. Suite 120 :: Germantown, MD 20874

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This is written out of order of what was done. Moved things around to help group similar things....but it may have muddied the process. Sorry for any confusion. I can clarify.
Also, I have not fixed the issue completely. I think much of it had to do with envelope questions. Both the U/R values used as well as the exposed slabs that I don't think are actually exposed. While the unmet hours are still ~4600 - think this is on the right track.
I'd advise using a text comparison tool on the inp files. Something like WinMerge will help show the differences.

I'll keep hunting, but wanted to pass along what I'd found thus far.

First question I would have is why a System 7? Show the model has 4 stories and is ~121k SF , which is below the 5story or >150k SF mark. Definitely will want to confirm that.

I was also confused on HVAC units and zoning. Systems 5-8 are a system per floor, so the System 1B and 2B should really be combined into the 1A and 2A systems. You'll also need a system for the basement/below grade floor. I did not rezone or change system types; just ran with it as is/was.

The EWall constructions are pretty poor. A U=0.313 is only an R=3.2 wall. Similar the roof is U=0.165 R=6.
Bumping the EWall and Roof up to Climate Zone 4 values and the heating goes down. These are the constructions I'd use to submit to LEED. Appendix G points out that all walls must be Steel-framed and Roof is Insulation Above deck. I added/modified insulation just to get something closer to what is required.
Another odd thing is that all of your floors appear to have exterior slabs. This doesn't appear to be correct. The should be internal floors. Modification of these reduces heating consumption in a big way. Shell 'EL1 Top' is/was correct. Modified Shell 'EL1 Ground Flr'. This was also leading to HUGE airflows in your HVAC units. This helped a ton there.

Zone Thermostat schedules and Indoor Design Temperatures.
The Zone thermostat schedules appear to not have any setback. Heat to 70F and Cool to 72F for all hours, yes? The Fan schedule does vary though. Just want to confirm as that is a bit unusual these days to not have a setback.
On the Zone Design Temperatures, I noticed these were set to 75F for cooling and 72F for heating. These need to align with the thermostat schedule setpoints for eQuest to properly size the equipment. So I set these to align with schedules; 72F cooling and 70F heating.
I reset throttling range back to default/2F. These should match proposed.


Discharge Air Temperature (DAT)
This was the largest change. For Heating, per Appendix G, the Discharge Air Temp is 20F above the zone setpoint. With a 70F heating setpoint, this means the DAT is 90F. Cant heat a zone to 70F with 60F air.

CFM. Appendix G requires autosizing. Removed all CFM values
Night Cycle Control = Cycle on Any
Zone, Flow/Area. Removed this as the airflow must be auto-sized. Unless - there is some hard flow rate rate in the proposed as well. Ex: hospital air flow for pressure dependent rooms.
Thermostats changed to 'Proportional' from 'Reverse Acting'.

Water Side - Hot Water
Per G3.1.3.3 its 180F supply, 130Freturn; thus a 50F delta. Change that on the hot water loop.
The baseline is also only allowed 2 Natural Draft boilers. G3.1.3.2. I removed Boiler #2.
They'll also only be 80% efficient, thus updated the EIR.
The Baseline is also auto-sized, so I removed the hard sizing and assigned a 0.50 sizing ratio.

Note: System over-sizing factors are only applied once. They can either be applied at the plant (boilers at 0.625 each, chillers at 0.575 each (assuming 2) OR 1.15 if only a single chiller) OR at the Air-Side units, with the plant equipment at boiler =0.50 and Chillers at 0.5 if 2, 1 if a single chiller or some other decimal if there are more than two chillers. G3.1.3.7. We have found it easier & more consistent to apply at the Air-Side, but it really is your choice.
If over sizing at the Air-Side, then set the over-all sizing factor =1.0. The cooling =1.15 and the heating =1.25.
Found the cooling sizing ratio =3.0. this should be either 1.15 or 1; depending on where sizing factors are applied.

CHW delta T=12F, per G3.1.3.8. Changed from 10F previously.
HW reset schedule modified to G3.1.3.4.
CHW reset schedule modified to G3.1.3.9

Mechanical Engineer, Energy Analyst

Henderson Engineers
daric.adair at

Licensed in KS

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