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Where to see ventilaion/fresh air load in eQUEST detailed report?

asked 2017-12-26 06:13:02 -0600

Yasin gravatar image

updated 2017-12-26 16:07:12 -0600

Hi,

I am confused in the detailed report of eQUEST. Actually I want to know the ventilation load but I don't think there is any separate report which contain the ventilation load. Generally It is recommended that subtract the Building load (LS-C) from Building HVAC load (SS-D) and you can have approximately fresh air load because system and other losses are low. But I don't think it is right and So I made to Model with and without the fresh air. I am going to give you some some number from my two model. (Single Zone with Standard VAV without heating)

With Fresh Air (load in kbtu/hr) LS-C Report Load is 235 (sensible = 214 and latent =21) SS-D Report load is 398 which is total building HVAC load. So as per the general practice ventilation load is 163 (398-235) which I think is higher number but anyways, lets accept it for time being.

But When I see my SV-A report the system capacity is 337 with 9385 CFM. The CFM is correct as I did the calculation considering building sensible load 214 but I don't know how eQUEST calculated the system capacity 337while my total building HVAC load is 398. And because of this I am having 361 Unmet hours. Then I went to Plant report and I found

PV-A report saying 341 loop capacity which I understand is calculated based on the system capacity (337) and chiller sizing is 349. But when I see PS-C report my chiller peak is 403 so i don't understand how chiller can operated beyond its capacity.

Now lets analyze the other model without fresh air LS-C report (235) is same which is correct but in SS-D report the building HVAC load is 282 so here is the confusion: If there is no fresh air why building HVAC load is not equal to LS-C load if losses can be neglected ( as I used zero losses as much as possible. And In SV-A system capacity is 291.7 though calculated CFM in this case is again correct and same 9385 CFM. But again why the different number in LS-C, SS-D, SV-A?

I know its a very big query but all I need is the understand the eQUEST calculation.

Thank you

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answered 2017-12-29 05:12:55 -0600

Joe Huang gravatar image

updated 2017-12-29 05:21:01 -0600

You're asking several different questions here, so I'll just address the ones on the differences between the loads reports in LOADS (LS-E, LS-F) and SYSTEMS (SS-A, SS-D), and how to find the fresh air load.

I do not recommend comparing the loads reports from LOADS to those from SYSTEMS because they're calculated very differently and serve very different purposes. The LOADS loads reports are tabulations of the heat flows into a space or building at the fixed reference LOADS temperature (Default is 70 F), with the heat flows assigned to heating or cooling depending on whether the aggregate loads that hour is positive (cooling) or negative (heating). The SYSTEMS loads reports give the heating or cooling input required for each hour into a zone to meet the specified set-point temperature. The differences are thus very striking: (1) the reference temperatures are quite different, (2) the LOADS loads have no deadband, (3) the attribution to heating and cooling are very different, (4) LOADS loads can be disaggregated to building components, but SYSTEMS loads cannot because the SYSTEM simulation works only at the space/zone level, and of course, (5) fresh air or any other load introduced by the SYSTEM simulation do not appear at all in the LOADS report. Therefore, trying to get a measure of the outside air load by comparing the SYSTEM to the LOADS reports is highly unreliable and can even be completely misleading.

However, there is a way to get the outside air load exactly, but it requires using the HOURLY-REPORT option in DOE-2 and then a little bit of postprocessing. In the HOURLY-REPORT specification, print out the Zone Temperature, Ventilation CFM, and Equipment Ontime for Heating and Cooling each hour. Then, you can calculate the Ventilation Air Load each hour as the temperature difference between the outside air and the zone times the CFM and the heat capacitance of air. I still remember that equation in IP as DeltaTxCFMx0.0128. If the equipment is on, it would be obvious to attribute the Ventilation Air Load as either Heating or Cooling, but what to do if the equipment is off? The best method I've found is to aggregate them in a cache that is then assigned to whichever mode the equipment next comes on. For example, if the HVAC is shut off at night, the cached Ventilation Air during those hours will be assigned as Heating Loads when heating comes on the next morning. You can think of that ventilation load as a morning pick-up load. If you throw away these ventilation air loads when the equipment is off, you will have underestimated their impact on the building load.

One last practical suggestion, you might also try the eQUEST-Users bulletin board because there seems to be a lot more eQUEST users participating there than here on Unmet Hours.

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Asked: 2017-12-26 06:13:02 -0600

Seen: 338 times

Last updated: Dec 29 '17