<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML xmlns:o = "urn:schemas-microsoft-com:office:office"><HEAD>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<META content="MSHTML 6.00.2716.2200" name=GENERATOR>
<STYLE></STYLE>
</HEAD>
<BODY bgColor=#ffffff>
<DIV><FONT face=Arial size=2>The SPACE loads are calculated at a CONSTANT
temperature all year, and should normally be specified as the average
temperature for the year (such as 73F). The ZONE loads take into account
the actual thermostat setting, changes in the setting (night setbacks/setups,
etc.), and deviations from setpoint. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Changes in setpoint cause mass effects to come into
play. For example, if a zone is held at 55F all night, and is then raised
to 70F the next morning, the HVAC system will have to warm the internal mass as
well as offset the envelope losses. As a result, the heating load after
the temperature setback is terminated will be greater than it would be if the
space were held at 70F all night. (Note that mass effects last for
multiple hours, and gradually taper off as the mass comes into equilibrium with
the new temperature.)</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Deviations in setpoint (and loads) occur because of
the system response to the load. For example, if the thermostat
setpoint is 75F during cooling, but the HVAC system is too small to
handle the load, then the actual zone temperature will float higher
than 75F; the higher temperature then acts to reduce the load. The actual
temperature will be the balance point between system capacity, envelop and
internal loads of the space, and mass effects within the space.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Air handler loads are a function of the zone loads,
latent cooling, duct heat gain/losses, fan heat, outside air introduced for
ventilation and/or economizer savings, reheat energy in VAV systems, mixing
losses in dual-duct systems, etc.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Loads on a boiler or chiller are a function of the
coil loads in airhandlers, pump heat, and piping heat gains.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>So the loads summarized in the LS-A, etc. reports
are space loads that occur at a constant temperature. They exclude all of
the mechanical effects of temperature swings, ventilation air, etc. that
are accounted for in the SS-A, etc. reports.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Given that the LS-** reports do not actually report
the true loads, are they useful? YES! You should always review
these reports when creating a new model. In addition to reporting lighting,
daylighting, and equipment energy, they are excellent reality checks
on the origin of the space loads. The reports give breakdowns on
loads arising from lights, equipment, people, infiltration, walls, windows,
roofs, etc. An abnormally large or small load in a given category is a clue that
there is a mistake in your model. </FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The SS-* reports summarize the response of the HVAC
system to the space loads. It is wise to acquaint yourself with all of
these reports. One of my favorite reality checks is the SS-F report
which reports the maximum/minimum temperatures within a given zone.
Temperatures too far beyond the thermostat settings are a sure sign that your
model is not working correctly (or if modeled correctly, a sure sign that the
HVAC system was not designed properly!)</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The BEPU report is another good reality check, as
it breaks down gas and electricity consumption into the major end-use categories
(lighting, misc equipment, heating, cooling, fans, etc.). Again, once you
have become practiced in knowing what buildings typically consume, abnormal
numbers can jump out at you. </FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=ordenes@ctcinternet.cl href="mailto:ordenes@ctcinternet.cl">Familia
Ordenes</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=Bldg-sim@gard.com
href="mailto:Bldg-sim@gard.com">Bldg-sim@gard.com</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, August 21, 2002 12:21
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [Bldg-sim] thermal balance loads
vs. system loads (PowerDOE)</DIV>
<DIV><FONT face=Arial size=2></FONT><FONT face=Arial size=2></FONT><BR></DIV>
<DIV><FONT face=Arial size=2>
<DIV><FONT face=Arial size=2><FONT face="Times New Roman" size=3></FONT>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN lang=EN-US
style="mso-ansi-language: EN-US">Hi,</SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN lang=EN-US
style="mso-ansi-language: EN-US"></SPAN><SPAN lang=EN-US>When I compare the
results from the Space Loads and the System Loads in
<STRONG>PowerDOE</STRONG>, I can see a difference between these values
(sometimes the Space Loads are bigger than the System Loads and sometimes<SPAN
style="mso-spacerun: yes"> </SPAN>not). I do not understand how an HVAC
system actually responds to building loads. How does the thermostat measure
the space temperature ?<SPAN style="mso-spacerun: yes"> </SPAN>Is this
hourly space temperature the same for the building loads calculation ? Can the
HVAC systems affects the space loads ?<SPAN style="mso-spacerun: yes">
</SPAN></SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN lang=EN-US
style="mso-ansi-language: EN-US"><o:p></o:p></SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN lang=EN-US
style="mso-ansi-language: EN-US">I understand these questions may not be easy
to answer, but these topics are under construction in the PowerDOE Help and I
would like to understand better the program. I would be very grateful
if someone could send me some information to clear my
doubts.</SPAN></P>
<P class=MsoNormal style="TEXT-ALIGN: justify"><SPAN lang=EN-US
style="mso-ansi-language: EN-US">Best regards.</SPAN></P><SPAN lang=EN-US
style="mso-ansi-language: EN-US">
<DIV>
<DIV><FONT face=Arial size=2>Martín Ordenes M. <BR>Departamento de Ingeniería
y Gestión de la Construcción.</FONT></DIV>
<DIV><FONT face=Arial size=2>Pontificia Universidad Católica de
Chile</FONT></DIV></DIV></SPAN></FONT></DIV></FONT></DIV><PRE>
==================
You received this e-mail because you are subscribed
to the BLDG-SIM@GARD.COM mailing list. To unsubscribe
from this mailing list send a blank message to
BLDG-SIM-UNSUBSCRIBE@GARD.COM
</PRE></BLOCKQUOTE><PRE>
===========================
You received this e-mail because you are subscribed
to the BLDG-SIM@GARD.COM mailing list. To unsubscribe
from this mailing list send a blank message to
BLDG-SIM-UNSUBSCRIBE@GARD.COM
</PRE></BODY></HTML>