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

Karen,

I've modeled kitchen exhaust in the past by making a tiny zone (~1m2) that contains and air loop with supply and exhaust fans.Â This recognizes that most kitchen makeup and exhaust systems are similar to a closed loop, with the makeup air introducedÂ at or near the hood and having very little interaction with zone heat transfer.

If you adopt that strategy, adding heat recovery is not Â difficult.Â Does that make sense to you?

p.s.,

To include the zone interaction with the portion of coking energy that does get into the zone, I put some of the cooking equipment heat (e.g., 10%) as a gas or electric equipment object in the zone and the rest of the heat in the zone or as an exterior equipment object.

Often the makeup air unit is controlled to have constant discharge temperature, so it's energy use is independent of the zone energy.Â If you put the cooking energy in the (tiny) zone directly and model the makeup unit as constant discharge temp, you may get a lot of unmet load hours (which is explainable to USGBC reviewers, but I try to avoid raising needless flags).Â That's why I'll make the cooking energy an exterior object as a norm.

On Fri, Apr 24, 2015 at 11:36 AM, Karen Walkerman kwalkerman@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Â

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
jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx

Website l Â LinkedIn

The truth is still the truth, even if nobody believes it.Â A lie is still a lie, even if everyone believes it.