Kitchen Baseline System

If an exception to G3.1.1 applies then you must use it.

G3.1.1 Exception d states: "For kitchens with a total exhaust hood airflow rate greater than 2400 L/s, use system type 5 or 7 with a demand ventilation system on 75% of the exhaust air. The system shall reduce exhaust and replacement air system airflow rates by 50% for one half of the kitchen occupied hours in the baseline design.".

In the proposed system the user can modulate the exhaust flow rate through the hood as he prefers, according to the requirements of the cooking activities.

I have some doubts.

Suppose that in the proposed model the exhaust hood has an airflow rate equal to 10000 L/s.

1.In the baseline building shall I model system type 5 or 7 (according to the building dimensions) and that system is controlled in order to control indoor air conditions (heating and cooling) and then the exhaust hood is modeled separately, as process ventilation (same fan power as in the proposed model)?

2. Shall system type 5 or 7 provide replacement airflow rate (equal to 7500 L/s during half of the kitchen occupied hours and 5000 L/s during the other half hours) and no extraction, since extraction is provided by the hood?

3. Shall the exhaust airflow rates in the proposed be modeled as in the baseline model (7500 L/s during half of the kitchen occupied hours and 5000 L/s during the other half hours)?

Best Regards

I would recommend checking out Pacific Northwest National Laboratory's 90.1-2010 PRM Reference Manual (https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-25130.pdf) which includes more detailed guidance about kitchen exhaust modeling requirements for both the Proposed and Baseline model. 

1. The baseline would be modeled with a separate exhaust fan, but it is not considered process and the fan power would be included in the baseline system fan power allowance from Section G3.1.2.10.

2. The exhaust hood airflows would be 10,000 L/s for 50% of the kitchen occupied hours and 5,000 L/s for the other 50% of the kitchen occupied hours. System 5 or 7 would provide replacement airflow of 7,500 L/s for 50% of the kitchen occupied hours and 3,750 L/s for the other 50% of the kitchen occupied hours.

3. The proposed should be modeled as it would be expected to operate in the design, but if this is unknown then the baseline schedule should be used (10,000 L/s for 50% of the kitchen occupied hours and 5,000 L/s for the other 50% of the kitchen occupied hours).

Thank you very much, Tyler!

As for the 1. point (“The baseline would be modeled with a separate exhaust fan, but it is not considered process and the fan power would be included in the baseline system fan power allowance from Section G3.1.2.10”) shall I calculate the fan power allowance according to the equation for VAV systems of TABLE G3.1.2.9 and for the calculation of A shall I consider the pressure drop adjustment for “Fully ducted return and/or exhaust air systems” + “Exhaust filters, scrubbers, or other exhaust treatment” (TABLE 6.5.3.1.1B)? Any rule in order to allocate the total power between the System 5 fan and the exhaust fan?

Cell D32 of the v4_Minimum_Energy_Performance_Calculator states:

Report exhaust fans not interlocked with HVAC operation (…) and exhaust fans nor required in the calculations (such as (..) kitchen hoods operating independently of the building HVAC system) in “Process Equipment”.

In the building that I’m modeling replacement air is provided by a dedicated Air Handling Unit, which operates when the hoods operate because it is needed by the chefs. Are in this case the kitchen hoods operating independently of the building HVAC system or not?

I see that “Fans – Kitchen ventilation” is reported separately in Performance_Outputs_1

G3.1.1 Exception d states also:

“The maximum exhaust flow rate allowed for the hood or hood section shall meet the requirements of Section 6.5.7.1.3 for the numbers and types of hoods and appliances provided for the in the proposed design.”

Therefore I have to consider Table 6.5.7.1.3. Where can I find the classification of the type of hoods and of the “Duty Equipment”?

I have found ASHRAE 154 here: http://sspc154.ashraepcs.org/pdf/STD154_2003.pdf

I have not found that information there.

Moreover, according to table 2b of ASHRAE 154 the minimum net exhaust flow rate for “Light Duty Equipment”, “Wall-mounted canopy” is 310 L/s per linear meter while the maximum according to ASHRAE 90.1 is 217 L/s per linear meter. I’m missing something, because it seems that the maximum is less than the minimum.

Best Regards

You would use the formuala for VAV systems if your Baseline system serving the kitchen is System Type 5, 6, 7 or 8, and you would apply any pressure drop adjustments that are applicable in the Proposed design. The fan power can be distributed as 50% supply / 50% exhaust, or using the ratios of the Proposed design.

In your case the kitchen hood is not indepenent of the HVAC system because they operate together.

The hood type and equipment duty definitions are in Section 3 of ASHRAE 154 under "hood" and "equipment", respectively.

I'm not sure why the maximum values from ASHRAE 90.1-2010 are lower than the minimum values from ASHRAE 154-2003. It is possile the minimum values have been reduced in more recent versions of ASHRAE 154. Nevertheless you should use the values from ASHRAE 90.1, not ASHRAE 154.

https://cdn2.hubspot.net/hubfs/458550/US%20DOE%2090.1%20article%20kitche...

This is a good reference for kitchen exhaust system. The takeaway is that the demand ventilation system is exhaust hood variable speed fan required by G3.1.1(d). system 5 doesn't seem to handle any make-up/exhaust air. It has a good explanation of what do 79%, 50% mean.

"Example B shows a kitchen with more than 5,000 cfm of hood exhaust. In addition to a limitation on makeup air, this kitchen requires an energy saving option. There is not enough transfer air to meet the 50% replacement air requirement, so a DVS is used. The makeup air unit also requires variable airflow control, interfaced to the exhaust hood with the DVS. In this example, only one of the two exhaust fans needs a DVS to control 75% of the exhaust airflow."