I know this topic has been beaten like..., but the results I have been getting for the ## hours on a model with several DOAS's are horrible, (getting a little delirious at this point). There is a DOAS for each system with a different schedule than the next. Each DOAS has an ERV which operates with a DH of 2.0btuh/hr in cool/heat and float.
I feel like the problem is within the dummy zone or the schedules.
When I assign the DOAS air to the SZRH unit as OA from System the cooling load shoots up by about 50%, (even when I remove the ERV the results are similar, increased cooling).
The building is in a moderate climate zone.
The DOAS fan schedule is set to on at the same time as the SZRH unit.
The heating energy is reduced when I assign the DOAS.
The problems I see are, to list a few;
The dummy zone has all of its hours outside of the throttling range no matter how it is assigned and no matter what the t-stat schedule I assign.
The load doesn't budge once I remove the DOAS from the model, only when I add it to the SZRH unit as OA from system.
The DOAS does not show any heating load, only cooling load all year long (again moderate climate with cold seasons).
DOAS's have been done before without this problem, maybe adding too much info this time.
*How is the DOAS operating in eQuest?
Taking a stab I assume it is bringing in the OA and cooling it or heating it to whatever the temperature set-points are. Depending on the schedules the temp could be floating most of the time. The air is then brought into your secondary system at set-point or floating point. The OA from the zones attached to the secondary system are replaced by the OA from the DOAS. (?) Then the secondary system does its thing as usual.
(Not sure what is happening with the dummy zone? Does DZ care it gets any air? Looks like it does because of the unmet hours. Does the secondary system pick up the air from the DOAS after it has traveled through a space and picked up load? The dummy zone has no load but it's temp is always above 85.)
Now for the cooling to be increasing, the air must be coming in to the secondary system warmer than usual during cooling hours. (usual being the raw temperature of uncond outdoor air). But the results seem extreme.
For the heating to be decreasing the air must be coming in warmer than usual for the secondary system, which it is based on SS-O.
Does anyone have experience with this and what could be going wrong?
*Or, can someone link me to a basic DOAS goby?
I have searched the archives but many of the DOAS questions have gone unanswered in the past.
Thank You
Joe Fleming
E.I., LEED AP BD+C, BEMP
Are you willing to share your .inp and .pd2 input decks? I would take a
quick look if you are.
Carol
A colleague of mine spotted that it appears that the model is cooling the outside air twice.
The outside air was assigned to the dummy zone and all of the zones of the secondary system, as I thought this was the correct way to do a DOAS and that the DOAS would override the secondary system OA reqs. But, it appears they just add, so upon deletion of the OA in the secondary systems spaces the cooling load matches more closely. (The slight increase left is due to the ERV serving a system that has zones in heating and cooling and there is some heating before re-cooling that is taking place).
Is it correct to only have the OA in the DOAS and blank out the zone OA?
Joe Fleming
E.I., LEED AP BD+C, BEMP
Remember that eQUEST doesn't /really/ do DOAS yet. All it does is set
the OA temperature for the borrowing zone using the OA-FROM keyword to
the RA temperature of the "lending" system (which is why it has to come
first on the system list).
I really hope this changes in future releases!
Brian, this interesting. What about the humidity properties? Does the
DOAS pass on the Return air humidity level, too? Can you tell me where
the explanation about the DOAS return air being assigned to terminal air
OSA input is located in the eQuest literature? It might hint at the
humidity conditions.
Kathryn Kerns
Is it correct then that one cannot use an ERV with a DOAS?
Based on below, if I have it right, the borrowing system will get its entering OA conditions from the RA temp of the dummy zone. If one wanted to supply conditioned air to a unit from a DOAS then they would need to set the space conditions of the dummy zone down to 55F or similar? If you set the dummy zone temperature range to be what you need for the given design, so that your "return" air or exhaust air to the ERV is of the correct enthalpy. How would the DOAS operate to maintain these conditions when the dummy zone has no load? Would the ERV exhaust conditions be simulated correctly?
It is appearing that eQuest does not allow much modeling flexibility when trying to simulate a DOAS.
Joe Fleming
E.I., LEED AP BD+C, BEMP