Hello Bill/James,
I have a typical situation for DOAS system that serves fresh air (100% OA) to corridor spaces in multifamily building. The DOAS unit is equiped with heat recovery wheel, and uses the exhaust air from apartments, i.e. exhaust from bathroom and kitchen rather than return air from corridor itself. How would i model the system that uses recovered heat from one system to another in the eQUEST.
Thanks in advance for your help.
Regards,
Vipul
I don't think building codes will allow you to do that, not easily
anyway. AnOntario/Canada perspective though. Each of the apartments
will be it's own fire compartment. Everything breaking this barrier
will need fire dampers. All fire dampers need man access. May be much
more trouble than it is worth.
Bruce Easterbrook P.Eng.
Abode Engineering
Thanks Bruce,
The project is located in NYC, and the DOB has already been approved the design. The intent is to recover the conditioned air from apartment and use it to preheat the 100% OA that will be supplied to Corridors using heat recovery wheel.
Thanks,
Vipul
Vipul,
Regarding your original question of how to model the systems, perhaps, you could consider the corridor loads as part of the apartments. Fixed lighting for the corridors could be assigned along with apartment lighting with an hourly schedule. O.A. and motor power assigned to the apartment systems?? I?d need to give it some thought.
If the design isn?t cast in concrete yet, how?s this for a potentially less expensive design to accomplish a similar result? This assumes the corridor supply units and exhaust fans are in fairly close proximity to each other, which they might be if you?re looking at a heat wheel. In a different life long ago I spent 17 years with Hilton Hotels. At two older properties in TX we had similar corridor supply units where the conditioned OA went under the guestroom doors as toilet exhaust make up. The rooms had fan coil units. If you looked at all the rooms, most of the time the toilet exhaust was good, clean air. We petitioned and got approval (there were precedents set by other companies also) from the building departments to duct the exhaust back to the supply units and created a return air system. We added smoke detectors and dampers to satisfy the fire/life safety folks. We also used activated carbon or Purafil? filters to clean up the returned air. We were also prepared to add ultraviolet lamps if necessary to satisfy any health concerns, but they weren?t necessary with the filtration we used. We were able to go from 100% OA to about 15%-20% OA, which in addition to the energy savings can make a difference in required plant capacity if you also need to address the central plant. The Marriott Marquis in Atlanta, which opened about 1980 was originally designed with a similar system, so there have been precedents. Since times have changed, an analysis of the capital & maintenance costs of the systems (heat wheel vs. filtration) would probably be appropriate.
Just my 2 cents worth.
Mike Busman
Michael R. Busman, CEM
Vipul,
If the supply air from the DOAS is at (or near) room temperature, and ?room temperature? is about the same in the corridor as in the apartments units, then in the model I would exhaust the air from the corridor that the air goes into. Keep in mind that the energy model does not have to replicate the exact systems in the building. The energy model is to estimate the energy use of the building. As long as the (simplified) modeled system uses about the same energy use as the (complicated) actual system you will still get reasonable results.
If the DOAS supply air temperature is cooler or warmer than room temperature to help meet part of the space loads, then it gets more complicated. Most energy modeling programs, with a few special exceptions, cannot have two air systems serve the same space. In cases like that I have modeled an energy recovery system for each apartment unit instead of one big DOAS system. As long as the energy consumption is on a per cfm basis, the error from this method will be minimal. In the model the terminal unit coils will take the entire load, even though in reality part of the load will be handled by separate coils in the DOAS. If the DOAS coils have different fuel sources (like DX vs. chilled water, electric heat vs. hot water), then this approximation will be off. There will be more error if the big system modulates to meet changing conditions due to the part load curves, but as long as the systems are full on/full off the error will be minimal.
I hope this helps. Simplify as much as you can and remember that you are estimating energy usage.
Keith Swartz, PE, BEMP, LEED AP