Kitchen Make-up air unit

Sometimes.

If the unit is only make up air for the exhaust air then it is process. If it does any additional space conditioning then it is not process.

If the MAU condition only the OA for all occupants need for all building zones, how should model such unit then?

this unit seem to not exist in system 1-8 in ASHRAE appendix G. Thus, there is no guideline for it.

Sounds like a dedicated OA system. If that is the case you simply do not model such a system in the Baseline.

Then, the proposed model will have additional fan power at the MOA unit. This could be the major disadvantage of DOA system, isn't it.

However, in the baseline, ASHRAE allows us to model the exhuast fan tied to conditioned space using the same fan power calucated be appendix G. In this case ASHRAE does not panalize the exhuast system but if the DOA fan does not reflect in the baseline, it seems we could lose the point becuase of this system. (but the simple exhuast fan doesn't) So, is it possible to show the saving of this system by model DOA unit for both baseline and proposed and used the fan power from ASHRAE appedix G for baseline.

Your system will not be disadvantaged...let me try and explain:

So ASHRAE fan power calcs are for units that are conditioning a particular zone(s). The power includes both supply and exhaust fans as they are present. At the end of the day the used energy is dependant on the pressure drop in the complete system and the relevance of whether or not there are duel fans, fans in series, exhaust and supply fans or only supply fans is largely irrelevant. All the fans in the system have to overcome the system pressure at a given flowrate, and that is what deturmines the system fan power. After that you can split it up as you feel appropriate.

Process load fans are fans which are not coupled to the conditioning System loop. For example, a conditioning system feeds 10 Air Change (ACH) into a hot kitchen to supply cool fresh air. The kitchen exhausts, exhaust directly to the outside with 30 ACH. So where does the makeup air come from? Let's say 20 ACH comes from open windows. You can then assign a process load power to the kitchen exhaust fans of 20 ACH at the exhaust system pressure drop, and an extra power of 10 ACH at the exhaust systems pressure drop to the AHU supply fan power.

I'm sure that will confuse most reviewers, so however you decide to appropriate the fan powers (not the flowrates), include a good narritive. At the end of the day it is most important to account for all the energy consumptions (regardless of whether they are process loads or regulated), and a good reviewer will know when they can "let it slide".

PS. as fan energy is directly proportional to flowrate at specific pressure, have a look at the credit you can get for fully ducted systems, filters, heat exchangers, etc.TABLE 6.5.3.1.1B

In the case of supply and exhuast fans of a conditioned space, ASHRAE will have the formula for system 1-8 to calculate fan power for a baseline. For example if the space has 1000 cfm supply and 100 cfm exhuast, in system 1-2 the fan power would be 0.0003 kW/cfm and make the supply fan power to be 0.3 kW and exhuast fan to be 0.03 kW.

Now, when you have the DOA unit, the proposed will have XXX kW for running the DOA fan. DOA usually supply the OA to many zone using single fan.So, there is no place to put such as fan in "baseline" model. That XXX kW will exist only in "Proposed" model and cause disadvantage (cause energy consumption in proposed but not baseline).

So should we model DOA in baseline? if yes, what would be the method to calculate fan power for the baseline then?

Baseline:
You definately should NOT model the baseline as DOA. You must use the same ODA amounts that you assign to the zone for the zone minimums equal to those of the proposed DOA system in the baseline model. As long as you assign seperate systems for "non-normal" zones as per G3.1.1, you shouldn't be getting into any control issues. The fan power is calculated as per ASHRAE 90.1 App. G3.1.2.9 as before. From memory, you are required to model an extract fan in the baseline model if you have one in the proposed design, but you can assign the total calculated fan power as you see fit. The baseline AHU also assigns to many zones. You usually have one AHU per floor.

So there is no place to assign any fan power that we spend in DOA for the baseline, then?

Any comment Marcus? really need your help

The calculations are completely independent - Baseline G3.1.2.9, Proposed as designed. There is no this for that kind of comparison. Design your overall Proposed system to used less fan energy than the Baseline allowance. and you will save energy. In almost all cases the Baseline allowance is very generous and you should be able to show savings.

Thanks, Marcus

Yes the kW/cfm of a baseline is generous but if the kW of fan increases EER of the baseline system also increase as well. EER must deduce fan power out of the calculation. Also, in system 5-6, the fan become VAV. Thus, the fan energy become less even though the kW/cfm is high. Am i correct?

Yes you separate the fan power in some of the baseline systems. A system 5-6 does become VAV which reduces the fans power in the baseline. In my experience the allowance is still pretty generous.