[Equest-users] [BULK] 4-Pipe Fan Coil vs. VAV

[Fleming, Joe]

Without looking at the .inp file, the basic things that will increase your maximum load on a cooling coil in this case are (and vice versa for the heating coil);

*         lower supply air temperature set-point

*         higher entering mixed air enthalpy

*         or higher airflow across the coil if it is auto-sized

The basic things that can increase your mixed air conditions are;

*         higher outside air enthalpy or return air enthalpy

*         higher quantity of outside air

*         higher space temperature (leading to a higher return temperature)

And the basic things that can lower the supply air temperature in eQuest are (aside from just lowering it manually);

*         Different control scheme selected (for cooling and heating coils, like SAT reset)

*         Different unit operation (eQuest has a basic control scheme for each unit type that you can view in the help file)

So, this leaves us with, most likely, different unit operations as the cause for the coil load increase.
The 4 pipe system would either cool or heat, but not both.  Whereas the VAV system is maintaining a constant SAT of around 55 degF at all times, and reheating this air in the zones that need heat.  This could explain why the heating load is much higher, because the system is heating 55 degree air (assuming no SA reset), instead of heating space air mixed with a little outdoor air.  As for the cooling load being 20% higher, maybe the auto sized airflow rate of the system increased.  Or the static pressure increased significantly causing a large heat gain across the fan and making the system have to cool to 52 degrees in order to get a 55 degree leaving air temp.  Finally , perhaps the absence of a non-coincidental load is causing a higher peak, the fan coils may have not been on all at once at any time whereas the VAV system is at least cooling the minimum airflows to 55 degF at all times occupied.

Hopes this helps you troubleshoot.  Good luck!

Joe Fleming
E.I., LEED AP BD+C, BEMP
Mechanical Engineer II

TLC Engineering for Architecture
Your 2030 Challenge Partner

800 Fairway Drive, Suite 250
Deerfield Beach, FL 33441-1816

phone:

954-418-9096

fax:

954-418-9296

direct:

954-418-4591

website:

www.tlc-engineers.com<http://www.tlc-engineers.com/>


[cid:image001.gif at 01CBC480.437DFFA0]<http://www.tlc-engineers.com/>

From: Edward Kucirek [mailto:kucirekengineering at hotmail.com]
Sent: Friday, February 04, 2011 3:25 PM
To: Fleming, Joe; equest-users at lists.onebuilding.org
Subject: RE: [BULK] [Equest-users] 4-Pipe Fan Coil vs. VAV

The load is that much higher. I am not looking at consumption. I am looking at SS-D.

Kevin Hupf, LEED AP

Kucirek Engineering, Inc.
7587 Main St.
Omaha, NE 68127
Ph: (402)951-0022
Fax: (402)951-0023
kucirekengineering at hotmail.com
www.kucirekengineering.com



________________________________
From: joe.fleming at tlc-eng.com
To: kucirekengineering at hotmail.com; equest-users at lists.onebuilding.org
Date: Fri, 4 Feb 2011 14:16:35 -0500
Subject: RE: [BULK] [Equest-users] 4-Pipe Fan Coil vs. VAV
The cooling/heating "load" is that much higher or the "energy" is higher.

Joe Fleming
E.I., LEED AP BD+C, BEMP
Mechanical Engineer II

TLC Engineering for Architecture
Your 2030 Challenge Partner

800 Fairway Drive, Suite 250
Deerfield Beach, FL 33441-1816

phone:

954-418-9096

fax:

954-418-9296

direct:

954-418-4591

website:

www.tlc-engineers.com<http://www.tlc-engineers.com/>


[cid:image001.gif at 01CBC480.437DFFA0]<http://www.tlc-engineers.com/>

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Edward Kucirek
Sent: Friday, February 04, 2011 1:25 PM
To: equest-users at lists.onebuilding.org
Subject: [BULK] [Equest-users] 4-Pipe Fan Coil vs. VAV
Importance: Low

I am running a simulation to compare various systems. When I run the 4-pipe fan coil and I look at SS-D I get a building load for heating and cooling with what it should be but when I use the same building and change the system to Standard VAV with HW and CW the building cooling load is 20% higher and the building heating load is 65% higher. Does anyone have any suggestions as why this would be happening?

Kevin Hupf, LEED AP

Kucirek Engineering, Inc.
7587 Main St.
Omaha, NE 68127
Ph: (402)951-0022
Fax: (402)951-0023
kucirekengineering at hotmail.com
www.kucirekengineering.com
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