<br><font size=2 face="sans-serif">Hi Dana,</font>
<br>
<br><font size=2 face="sans-serif">Is your t-stat range a cooling or heating
range? If your system involves both heating and cooling, you will
need a setpoint temperature for both. Other than unitary systems,
your heating and cooling setpoints cannot be the same because the t-stat
will tell its controllers that it both needs to heat and cool to reach
setpoint. In eQuest, I believe the defaults are around 68 F for heating
and 74 F for cooling, which is typical for new systems.</font>
<br>
<br><font size=2 face="sans-serif">As far as letting the temperature float,
there are a couple of ways to do this:</font>
<br><font size=2 face="sans-serif">1. </font>
<br><font size=2 face="sans-serif">Setpoints can be scheduled with a BAS.
Usually, this includes an occupied setpoint and an unoccupied setpoint
setback. For example, a 74 F occupied cooling setpoint and an 82
F cooling setpoint setback after 7 pm. In eQUEST, this can be done
by editing the thermostat schedules. I'm guessing this is not what
you're looking for, but I'm throwing it out there just in case :)</font>
<br><font size=2 face="sans-serif">2.</font>
<br><font size=2 face="sans-serif">Most HVAC controllers are proportional
(P) controllers, which means that they control the HVAC equipment in a
proportional response to the difference between the sensed temperature
and the setpoint. An inherent property of proportional controllers
is that they cannot hit their setpoint exactly, but there will be some
offset. How much this offset is depends on the gain of the controller
when it is programmed by a technician. There is usually a trade-off
between offset and response time. In eQUEST, the offset is called
"Throttling Range" and is accessible in the Basic Specifications
Tab of the Zones dialog. So, a t-stat can be programmed to have a
greater offset or throttling range and the temperature will float more
around each setpoint. For example, if you increase the throttling
range to 4 R in eQUEST with a cooling setpoint of 74 F, the thermostat
will signal 100% response at 76 F and 0 response at 72 F. This will
result in an air temperature which floats more than a system with a throttling
range of 2 R. You may see building occupants complain more about
inconsistent temperatures with an offset of 4 R vs 2 R. Higher end
facilities will sometimes be equipped with a proportional-integral-differential
(PID) thermostat, which eliminates the offset of the proportional controller.
To model a PID controller in eQUEST, you simply reduce the throttling
range to a minimal value.</font>
<br>
<br><font size=2 face="sans-serif">Keep in mind too that when doing a simulation
like this, eQUEST is an hourly steady-state simulation engine with the
ability to approximate some transience. In reality, HVAC controllers
sample at a much faster rate than once per hour, and their response times
are much greater than instantaneous. Also, unfortunately, you cannot use
this as an ECM for LEED as they require equivalent t-stat setpoints in
baseline and proposed cases. Good luck!<br>
</font>
<table>
<tr>
<td bgcolor=white><font size=2 color=#808080 face="Verdana"><b>Aaron Powers</b></font><font size=3>
</font>
<tr>
<td bgcolor=white><font size=1 color=#808080 face="Verdana"><b>Johnson
Controls | Building Efficiency</b></font><font size=3> </font>
<tr>
<td bgcolor=white><font size=1 color=#808080 face="Verdana">Energy Solutions
Engineer</font><font size=3> </font>
<tr>
<td bgcolor=white><font size=1 color=#808080 face="Verdana">6935 Appling
Farms Pkwy # 112, Memphis, TN 38133</font><font size=3> </font>
<tr>
<td bgcolor=white><font size=1 color=#808080 face="Verdana">901 359 4255</font><font size=3>
</font>
<tr>
<td bgcolor=white><a href=mailto:aaron.powers@jci.com><font size=1 color=blue face="Verdana"><u>aaron.powers@jci.com</u></font></a><font size=3>
</font></table>
<br>
<p><font size=3> </font><font size=2 face="Calibri">We are interested
in modeling an ECM where we allow the temperature to float between a larger
range (70-74 or 70-76) versus a tighter range (say 71-73). I would like
to compare variations in building energy consumption for a few different
t-stat ranges. The model itself was built previously, so I’m hoping this
might just involve changing a couple numbers. Has anyone done this? Any
input would help. Thanks,</font>
<br><font size=2 face="Calibri"> </font>
<br><font size=2 face="Calibri">-Dana </font>
<br><font size=2 face="Calibri"> </font>
<br><font size=1 color=#5f5f5f face="Arial"><b>Mr. Dana Etherington, E.I.T.,
LEED AP BD+C </b>| <b>CRB </b>| One Kendall Square Ste B2202 | Cambridge,
MA 02139</font>
<br><font size=1 color=#5f5f5f face="Arial"><b>Main:</b> 617-475-3050 <b>|
Direct:</b> 617-475-3061 | <b>Mobile:</b> 617-583-3009 | <b>Fax:</b> 617-475-3052
| <b>Ext: 6061</b></font>
<br><font size=1 color=#5f5f5f face="Arial"><b>Email:</b> </font><a href=mailto:dana.etherington@crbusa.com><font size=1 color=#5f5f5f face="Arial"><u>dana.etherington@crbusa.com</u></font></a><font size=1 color=#5f5f5f face="Arial">
| </font><a href=http://www.crbusa.com/><font size=1 color=#5f5f5f face="Arial"><u>www.crbusa.com</u></font></a>
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