Re: [EnergyPlus_Support] New Feature Request - "Return Air Fraction" and "Exhaust Air Fraction" for Internal Loads?

I propose a summary:

Energy used by kitchen equipment normally generates both sensible and latent (moisture) components. Both should be accounted for.
Kitchen equipment that is under an exhaust hood loses energy to the outdoors directly (through the hood) and into the zone of which it is part. Both should be accounted for, although the hood component is very dominant (~90%), assuming that the hood is designed and working properly.
Because the (~90%) kitchen equipment energy passing through the hood exhaust does not affect the zone heat balance, it is not a good idea to place a heat source (e.g., a lighting object) in the zone because it will result in skewed energy use for the zone heating / cooling system.
Similarly, if the makeup air system for the exhaust hood discharges very close to the hood (or, as is common in USA, is actually part of the hood), the air from the makeup unit should not affect the zone heat balance (or its unmet load hours).
Kitchen equipment follows a different schedule than the zone around it, normally having distinct peaks that center around peak food preparation (e.g., early morning for a bakery, lunch or dinner hours for a restaurant, etc.)
There may be other criteria, but I ran out of ideas this morning...

For the reasons above, I have adopted this strategy for designs that use a makeup air unit which discharges its air very close to the exhaust hood:

Create a small, separate zone for the makeup air unit and exhaust (including the hood) This keeps the heat balance for the kitchen equipment separate from the adjoining kitchen zone.
Control the air loop of the makeup air unit with a constant temperature discharge or outdoor air reset control, whichever is used by the design.
Schedule the makeup / exhaust for actual operating hours.
Assign the kitchen equipment energy (sensible and latent) which is exhausted to an Exterior:FuelEquipment object so that its energy is accounted for, but does not affect a zone.
Assign the remaining kitchen equipment energy to the main kitchen zone (so that its energy does affect the zone) using OtherEquipment for latent energy)
If heat recovery is part of the design, it can be included in the makeup / exhaust air loop.

There. I have it off my chest and hope it is clear :). The previous posts on this thread did not seem to capture all of the elements, so I hope this helps condense and organize them.

On Mon, Apr 27, 2015 at 11:39 PM, 'jeannieboef@xxxxxxxxx' jeannieboef@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Lighting doesn't produce moisture, else it would work.

Mit freundlichen Grüßen- Sent from my iPhone (excuse the brevity)

i. A.

Jean Marais

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Tel. +49 30 6706662-23

On 27.04.2015, at 23:26, "Jason Quinn jason.e.quinn@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Couldn't you just model the kitchen equipment as lighting? i.e. set the power equal. Then you could specify the fraction. I know the meters would be wonky but custom meters are pretty easy to do.

Jason Quinn
+64 21 1846 911

On Tue, Apr 28, 2015 at 12:07 AM, Karen Walkerman kwalkerman@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Awesome! I'll do that.

On Apr 25, 2015 8:55 AM, "Linda Lawrie linda@xxxxxxxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

I believe you can enter a new feature request directly into the github system for EnergyPlus.

At 09:36 AM 4/24/2015, Karen Walkerman kwalkerman@xxxxxxxxx [EnergyPlus_Support] wrote:

I'm currently modeling a few buildings where the design team wants to explore the effectiveness of heat recovery on kitchen exhaust hoods.

In the DOE Commercial Reference Buildings, kitchen cooking equipment - 70% of the energy is modeled as "lost." Â Some of this energy is truly "lost" to the food being cooked, but much of it is captured and exhausted by hoods.Â It is not mixed with the zone, but in the model, it is captured by a system and should be modeled as such.

When modeling lights and refrigeration equipment, we are given the option to specify a "return air fraction" - a portion of the heat that is transferred directly to the zone return air.Â It would be awesome if this option were added to the following objects:

ElectricEquipment
GasEquipment
SteamEquipment
HotWaterEquipment
OtherEquipment

It would also be great to have an "Exhaust Air Fraction" option - so that some of the heat generated could be assigned directly to the exhaust air node.

While the need to model kitchen exhaust heat recovery illuminates the limitation within EnergyPlus, it is a limitation in accurately modeling kitchen energy use even without heat recovery.

Thanks!

Karen

James V Dirkes II, PE, BEMP, LEED AP
CEO/President
The Building Performance Team Inc.
1631 Acacia Dr, GR, Mi 49504

Direct: 616.450.8653
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