Secondary Loop Valve Type

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Hi eQUESTers,

For a secondary loop, there is an input for valve type - either three way
or two way. Can anyone provide a schematic or quick explanation of the
difference between how these two valves control the flow from the primary?
Is this input assuming there is a valve at the secondary loop connection?
If there is a simply a tee at the secondary connection, can the valve head
input be zero?

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Darryl,
A three-way valve will maintain constant total branch or loop flow by
modulating the flow to either the coil or directly to the return line. A
two-way valve will modulate open or closed to maintain a flow or
temperature (usually leaving air temp), as it closes it will reduce the
total loop or branch flow proportionally. 3 way valves are not generally an
acceptable choice because they run counter to the desire to reduce flow to
reduce energy consumption. These valves are usually at the coil but can be
at the primary secondary interface they perform the same function in
general at either location. Smaller systems that might lack sufficient
diversity to ensure a minimum level of system flow sometimes use these
valves to ensure that the pumps don't "dead-head".

David Berty, P.E.
Baseline Energy Consulting
317.220.9272

On Aug 23, 2016 2:17 PM, "Darryl Kasun via Equest-users" <

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Joined: 2016-07-15
Reputation: 400

Hi David,

The flow in the secondary loop definitely varies based on differential
pressure setpoints. There are two way valves at reheat coils, reflected
ceiling plans, etc. And I've entered this input (two-way valve) at the
thermal zone level.

I guess I'm confused at the circulation loop level. In this window, there
is also an "valve type" input for the secondary loop. I know the primary
loop is constant and the secondary loop is variable so I'm thinking this
input should be "two-way valve" again. These two inputs seem redundant to
me...

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Sounds to me like you have a three way valve at the primary-secondary
interface. You said that the primary was constant, that most likely means a
three way valve to ensure that primary pumps never vary in flow. What
doesn't go to the secondary loop will return to the chiller. Does that make
sense in your project design?

David Berty, P.E.
Baseline Energy Consulting
317.220.9272

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Yup absolutely. But there's no real valve at the primary/secondary
connection - just a tee.

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Joined: 2016-07-15
Reputation: 400

Oh OK, I'm catching what you're pitching now.
I would enter that as a three way valve with no head loss as you suggested.

Anybody else done something different with this?

David Berty, P.E.
Baseline Energy Consulting
317.220.9272

via Equest-users's picture
Joined: 2016-07-15
Reputation: 400

Great - that makes sense to me - thanks for you help David!

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Joined: 2016-07-15
Reputation: 400

If the primary loop is constant flow and the secondary loop is variable flow, I also suggest using a three-way valve. See DOE22Vol2-Dictionary_48r.pdf, page 241. DOE2 assumes a valve exists if the secondary loop has its own pump.

Christopher Jones, P. Eng.
Rowan Williams Davies & Irwin Inc.
Consulting Engineers & Scientists
901 King Street West, Suite 400, Toronto, Ontario, M5V 3H5
T: (519) 823-1311 ext 2052
M: (416) 697-0056

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Joined: 2016-07-15
Reputation: 400