Hi,
I am working on a dining facility where we have two makeup air units serving the kitchen hoods. The units in the proposed case are equipped with chilled water coils served with the building air cooled chiller to tamper the air to 80 degree F. the units are considered as process and are supposed to be modeled identical in the proposed and the baseline case. Since the building chiller is a high performance magnetic chiller serving the whole building what is the baseline piece of equipment that needs to be modeled to serve the makeup units since the baseline system is type 3 dx packaged units.
Is it an air cooled chiller with ASHRAE 90.1 performance and sized for the coils capacity?
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HOUCINE TLEMSANI
Mechanical DesignerMEP Engineering Solutions, Inc
14 thumbs up
September 17, 2014 - 10:00 am
Any guidance would be appreciated. Thanks.
Victoria Watson
AECOM4 thumbs up
September 17, 2014 - 11:01 am
Hi Houcine,
One way of thinking about this (I am be wrong) is that perhaps the makeup units are not classed as process energy if they have chilled water coils as they are conditioning the space. However the outside ventilation rates should be the same in both building so the baseline building would also need to makeup this air. If the baseline system is type 3 DX packaged units, then this serves the space but with the outside air rate to match the proposed building (E.g. there will be a constant outside air during times the makeup unit is in operating in the proposed at that rate).
Anyone have any other thoughts? I have come across similar tricky situations with makeup air in buildings.
HOUCINE TLEMSANI
Mechanical DesignerMEP Engineering Solutions, Inc
14 thumbs up
September 19, 2014 - 12:08 pm
Thanks Victoria
The kitchen makeup units are serving 80% of the hood required makeup the rest is coming from the building system and are not really conditioning the space. The only reason the air is tempered to 80F is for the cooks safety purpose and RFP requirement. All the hoods ventilation system is for kitchen heat and smoke removal. Therefore I believe that it is process, (correct me if I am wrong).
My question is that if it is process how will it be modeled in the base line and what type of equipment will be modeled for the chilled water coils. Since the base line model does not have a chilled water system.
I guess the only way is to compare it to a chiller with ASHRAE 90.1 performance and claim savings.
Anyone had this situation?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
September 24, 2014 - 2:39 pm
Two options come to mind.
One - model a little mini-chiller identical to the Proposed in the Baseline. This may present some major issues in certain software.
Two - calculate the overall seasonal system efficiency for the Proposed chilled water system (pumps, etc.) and apply that to a DX system with a flat curve.
Since it is process you can only claim savings through an exceptional calculation. Section 6.5.7.1 prohibits the use of cooling in kitchen make-up air hoods over 5000 cfm. If that is the case then the proposed should be modeled as designed and the baseline should be modeled without any cooling.
HOUCINE TLEMSANI
Mechanical DesignerMEP Engineering Solutions, Inc
14 thumbs up
October 1, 2014 - 2:42 pm
Thanks Marcus
ASHRAE 90.1 section 6.5.7.1 allows the cooling or heating in kitchen make-up hoods under the Two exceptions a and b and almost all engineered hoods will meet exception b. we are in such hot and humid climate that it is almost becoming a requirement to provide some sort of cooling thru the make-up to provide some comfort in the kitchen. That said. If I am claiming saving thru exceptional calculations. Can I model the baseline make up with a chiller that meets the minimum requirement of 90.1 or am I missing something.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
October 10, 2014 - 3:54 pm
You could use one of the two methods mentioned above but substitute the a similar type of chiller's efficiency from 90.1 as the baseline. Makes sense to us as a reasonable rationale for the baseline.