[Equest-users] T-Stat is acting Screwy

David Bastow dbastow at mcclure-engineering.com
Wed May 19 08:13:47 PDT 2010


Rob,
 
I have a number of questions:

1.	
	Do you have many lab hoods?  And are exhaust and make-up air
revised for the lab hoods at the night set back time?
2.	
	What is the percent of outside air to the lab?  Does this
percentage change during the night set back time?
3.	
	Do you have a pre-heat or exhaust heat recovery and pre-cooling
on your make-up air?  What is the temperature setting of this pre-heat
or heat recovery and pre-cooling?  Does the temperature settings on
these change at the night set back time?
4.	
	Do you utilize an air or water side economizer for 1st stage
cooling?  Does this use change any at night set back time?
5.	
	Does the fan run continuously day and night?  Have you ran
models with the fan running continuously, and with fan cycling based on
demand at night and off completely at night, to see how the results
compare?
6.	
	Do you have a internal load watts per square foot and latent
load on the space from interior lighting and equipment?  Do these loads
change at the night set back time?
7.	
	Are you adding humidification or dehumidifying the space based
on some humidity settings?  Does the humidity settings change during the
night set back time?

One of these things is probably causing the increased chilled water
cooling load.  Often if you have high internal loads, even at night,
then changes to the fan cycling and the amount of outside air brought in
at night, will increase the chilled water cooling load.  I would review
all of these areas and run various test models to see how they each
affect your energy usage when modified.
 
Our firm just completed modeling some very large lab facilities with
more than 55 exhaust hoods in the building, with high internal loads
24/7 and 100% outside air.  As long as the models are set up correctly
they are normally right.  It takes some real design and thermal dynamic
thought and often may models to really get your mind right with what is
truly going on with the facility.  Its important to keep an open mind to
what is going on.  Having been doing computer hourly modeling for over
17 years, it is often easy to think you have a handle on what is going
on with the building, but it is important to keep an open mind and
investigate all the different avenues that you can think of until figure
out what is going on.  I have 99% of the time that I have blamed the
screwy program having problems that I have found that I just didn't look
at all the different angles enough.
 
David A. Bastow 
McClure Engineering, Inc.  
<http://www.mcclure-engineering.com/>  

________________________________

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Rob
Hudson
Sent: Wednesday, May 19, 2010 7:46 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] T-Stat is acting Screwy


I have a lab space that is kept between 73 and 70 degrees all year long.
One of my parametric runs has the cooling and heating T-stat schedules
changing to have night time setbacks to 80 and 60, respectively.  When i
use these, i get more energy spent overall.  specifically, i have a
chilled water meter, steam meter, electric meter and hot water meter to
monitor everything.  The chilled water increases while the others
slightly decrease when i use the set back schedules.  Any ideas?

-- 
Rob Hudson

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