I doubt I'm the first to think of this but I don't recall it being discussed on the List. Simply put, you can model a DOAS system by assigning it to the plenum spaces above occupied spaces, and putting all OA loads in the plenum zones.
I propose the following workaround for modeling dedicated outdoor air systems (DOAS) in eQUEST/DOE-2.2:
- Model all shells/floors with plenum spaces if they are served by a DOAS
- Change the plenum zones ZONE: TYPE to "Conditioned"
- Leave the plenum zone COOL-TEMP-SCH and HEAT-TEMP-SCH as "undefined" (no zone control over the DOAS operation)
- Pick DESIGN-COOL-T and DESIGN-HEAT-T values for the plenum zones that match the likely DOAS supply air temperature range
- Create the DOAS as a new SYSTEM (TYPE = [whatever is appropriate])
- Assign the DOAS to the plenum zones above the conditioned zones that it actually serves
- Assign outdoor air only to the plenum zones, representing the outdoor air requirement of the conditioned zones below
- Create/modify internal walls between plenum zones and zones below, making them "Air walls"
This method has the following advantages:
- No exceptional calcs or separate models needed (but see "Conditioned area" comment below)
- All DOAS systems can be modeled as designed, within normal eQUEST constraints
- A single DOAS system can supply ventilation air to multiple zones/systems
- DOAS system operation and ventilation supply can be independent of the other systems serving the zones
- Return air temperature to the DOAS closely follows that of the occupied zone, for accurate heat recovery simulation
- Zonal systems "see" the space load from ventilation air that is not supplied at a "zone-neutral" temperature
- DCV can be modeled, but people need to be assigned to the plenum spaces instead of the occupied spaces below (which might also be a disadvantage of this method)
- No ventilation load changes need to be made to create the LEED Baseline from the Proposed design model, but the plenum zones need to be assigned to the baseline systems that serve the zones below.
...but has these disadvantages or does not solve these problems:
- Conditioned floor area reported (such as in LS-C) is incorrect. Subtract the area served by the DOAS (as reported on SV-A).
- Latent heat transfer is not simulated across interior walls. Ideally, latent loads should be assigned to the plenum spaces to represent the portion of non-ventilation latent loads handled by the DOAS.
- Plenum space FLOOR-WEIGHT may need to be adjusted for realistic lag time and peak load damping (I haven't thought this out yet)
Please discuss!
~Bill
William Bishop, PE, BEMP, BEAP, LEED AP
