[Equest-users] Modeling air-side economizer

[Chris Baker]

That is correct!  The existing air handlers were once connected to heating coils because of the cold climates here in Alaska.

We disconnected the heating coils, left the existing VFD's and connected the two side-by-side units on a control schedule on-demand cooling.

The systems are literally "air side" only.  There are no coils connected for heating or cooling.

Sys enable if OA is above 55F

Fans run if room temp is above 68F
Fans shut off if room temp is below 65F

The summer schedule is to run in occupied mode when the average space temp exceeds 76F
In unoccupied mode the system will run for 2 hours if OA temp is greater than 55F but under 65F.

A min setpoint of 60F is always maintained.
S/A is modulated with VFD's to maintain 0.02 in WC greater than outdoors.

These are not in operation during winter months.

The project got new air handlers to supply heated air to the building (System 1 and System 2 in my current proposed model).  But there are also baseboards on a loop.

-Chris


From: Sami, Vikram [mailto:vikram.sami at zgf.com]
Sent: Wednesday, March 04, 2015 9:59 AM
To: Chris Baker
Cc: equest-users at lists.onebuilding.org
Subject: RE: Modeling air-side economizer

Chris,

Maybe I am misunderstanding your question. An air-side economizer (in my mind) is something that operates in cooling mode only - when you need cooling and the outside air is cool enough to supply that without running your compressors or needing chilled water.

If you are running a unit ventilator - there is no cooling equipment. So your ventilator will be supplying outside air without cooling (i.e. economizer mode) whether you like it or not. Why would you need a stand alone economizer?

If your intent is to have mechanical cooling for this system (where you would need an economizer), then maybe the unit ventilator is not your best choice of equipment.

Vikram Sami
AIA, BEMP, LEED BD+C
Associate Partner



ZGF ARCHITECTS LLP
T 206.521.3509 E vikram.sami at zgf.com<mailto:vikram.sami at zgf.com>
925 Fourth Avenue, Suite 2400
Seattle, WA 98104


From: Chris Baker [mailto:CBaker at cci-alliance.com]
Sent: Wednesday, March 04, 2015 10:53 AM
To: Sami, Vikram
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: RE: Modeling air-side economizer

Sami,

Thanks for your reply.

What would be the best approach in your opinion?

I could technically model as different system type (packaged single zone, etc.).  And apply cooling per the economizer schedule to the existing systems individually.
That way the system is accurately modeled.

OR I could keep the system as it is now, with unit ventilator, and add a separate stand-alone economizer system that would apply to all the zones.

Thank you!

-Chris

From: Sami, Vikram [mailto:vikram.sami at zgf.com]
Sent: Wednesday, March 04, 2015 8:33 AM
To: Chris Baker; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: RE: Modeling air-side economizer

This is probably happening because the System type: Unit Ventilator is a heating only system (so in essence you are always in economizer mode - there is no cooling modeled).

Vikram Sami
AIA, BEMP, LEED BD+C
Associate Partner



ZGF ARCHITECTS LLP
T 206.521.3509 E vikram.sami at zgf.com<mailto:vikram.sami at zgf.com>
925 Fourth Avenue, Suite 2400
Seattle, WA 98104


From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Chris Baker
Sent: Tuesday, March 03, 2015 7:57 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Modeling air-side economizer

Does equest require a certain HVAC "System Type" before you can add specific air-side economizer inputs?

I'm currently showing "Unit Ventilator" system type in proposed.
Equest won't allow me to add air-side economizer cycle data (dry bulb shutoff, etc...)

Also, would it be reasonable to keep the current systems as-is in equest...
Then add a "sum" system separately to allow ALL zones to receive air-side economizer cooling?
(with sum system on economizer schedule only)

I should also mention that what I'm modeling are the building's pre-existing air handlers with VFD's and no coil attachment.
Our renovation project involved keeping the old AHU's but with on-demand cooling controls.

Chris Baker
CCI CAD Drafter


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