[Equest-users] Supply CFM based on heating / cooling mode

[ToddGibson at Eaton.com]

Thanks for the suggestions.  It appears that the MIN-FLOW-RATIO is overriding the heating flow rates even though the documentation doesn’t make that clear.

Because of the occupancy pattern of my building, the majority of the occupied hours are in the heating season so I have set the supply CFM to be the heating CFM rather than the cooling CFM as a workaround for now.

 

Todd Gibson

 

 

From: Nick Caton [mailto:ncaton at smithboucher.com] 
Sent: Wednesday, June 20, 2012 4:11 PM
To: Gibson, Todd; equest-users at lists.onebuilding.org
Subject: RE: Supply CFM based on heating / cooling mode

 

I have a few thoughts/ideas, in no particular order – maybe something here helps:

 

Note these flow inputs exist for the system and zone level – you could be editing one and looking at results for the other.

 

I think MIN-FLOW-RATIO (minimum flow ratio) can override the (optional) heating minimum flow input.  Required ventilation capacities can override either as well if I’m not mistaken – maybe worth checking.

 

Just to point out:  a MIN-FLOW-RATIO of 1.0 means the flow will go no lower than 100% of what’s specified (or calculated) for SUPPLY-FLOW.  Consider carefully if and where that should apply to fans in the system you’re modeling.

 

Another thought is at least some of these zonal inputs will default to the system’s values if you aren’t specifying them separately… perhaps your central system is in cooling, using 1.00, while your terminal units are in heating and you end up with a conflict?

 

~Nick

 

 

 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of ToddGibson at Eaton.com
Sent: Tuesday, June 19, 2012 10:27 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Supply CFM based on heating / cooling mode

 

Hi,

 

I’m trying to specify separate, constant CFMs for heating and cooling mode operation (Ex:  5,000 Heating & 7,500 Cooling).   

 

The system I created is Variable Air Volume which serves multiple thermal zones.

The Fan Flow Parameter MIN-FLOW-RATIO is set to 1.00.  I read this as the minimum supply CFM during cooling mode.

The Fan Flow Parameter HMAX-FLOW-RATIO = 5000/7000.  I read this to be the maximum supply CFM during heating mode.

The Fan Flow Parameter HMIN-FLOW-RATIO = 5000/7000 -0.01.  I read this to be the minimum supply CFM during heating mode.

 

But from the hourly report the CFM supplied, defined by SUPPLY-FLOW = 7,500, is the cooling quantity during heating mode when I would have expected it to be 5,000.  As far as I can tell no flows are specified at the zone level that would override it.  Any thoughts on things to look at would be greatly appreciated.

 

Thanks, Todd

 

 

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