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<P><FONT size=2>I have attached my replies in the text.<BR><BR>-----Original
Message-----<BR>From: stvgates@pacbell.net [<A
href="mailto:stvgates@pacbell.net">mailto:stvgates@pacbell.net</A>]<BR>Sent:
Tuesday, April 13, 2004 8:49 AM<BR>To: bldg-sim@gard.com<BR>Subject: [bldg-sim]
Radiant Heating/Cooling<BR><BR><BR>I also have some questions on radiant heating
that I hope someone can<BR>answer:<BR><BR>1. It is well understood that,
for a given comfort level, a higher mean<BR>radiant temperature allows for a
lower ambient temperature. <FONT color=#ff0000>This is not quite true. The
radiant component either heating or cooling can balance the mean radinat
tempertaure exchange in a space. Onec the MRT has been balanced, incresed for
heating or lowered for cooling then the space temperature can be adjusted to an
optimum temperature as long as the occupant comfort remains within PMV=/- 0.5.
Typical values for heating would be about 68F and for cooling about
78F.</FONT></FONT></P>
<P><FONT size=2>This suggests<BR>that one can lower the thermostat
setpoint. <FONT color=#ff0000>yes</FONT> But, if the thermostat
is<BR>lowered to 65F, and the ambient temperature is 66F, then the radiant heat
is<BR>off, and the mean radiant temperature drops. <FONT color=#ff0000>Not
if the solar gain to the space remains.</FONT></FONT></P>
<P><FONT size=2>So are the people comfortable<BR>when the space is 66F<FONT
color=#ff0000> This would be calculated, my gut feeling would be that 66F would
be pushing the minmum PMV of - 0.5.</FONT>, or do they raise the
thermostat?<FONT color=#ff0000> most propbably but to what tmperature, most
humans would reset to say 70F and this would be a slight overkill, us engineers
would be happy with 68F. The point here is the very gery area we now find
ourselves in. The new ASHRAE standard 55 reverts back to the PMV +/- 0.5
identical with ISO 7730 which then states comfort criteria for a space as
opposed to dry bulb temperatures being used to dictate space conditions and
sometimes hopfully comfort.</FONT><BR><BR>2. Granted, infiltration heat
losses can be lowered by reducing the air<BR>temperature. <FONT
color=#ff0000>Infiltration will not be reduced by lowering the air tempertaure
however the effect of possible infiltration would be reduced. The heat losses
would be reduced if lower temperatures were used.</FONT> But the radiant
heat source is also warming the room surfaces,<BR>including the exterior wall
surfaces and window surfaces. <FONT color=#ff0000>Good point, however,
most programs and engineers are incapable of calculating this. My experince has
been that the inside surface temperature is calculated using the component u
value, the temparture differential across the component and then using the heat
transfer coefficient of the inside surface to calculate the inside surface
temperature. There is another longer explanation which is basically the
diffrenece between the responese method of calulation against
forward finite element. </FONT>If those surface<BR>temperatures are then higher
than they would be with a convective heating<BR>system, their conduction losses
are now greater, even though the air<BR>temperature is lower. <FONT
color=#ff0000>correct, but what are we heating the space or the losses. In
simple terms if a space were calculated to maintain say 70F at outside
conditions of say 20F ( not for californians), then the dalta t = 90F and the
heat loss from the space is calculated. Now if the inside space temperature is
reduced to say 68F then the delta t= 88F and the calculated heat losses
would be slightly less. The discussion being that the heat losses to the
exterior would be slightly higher if the surface temperatues were higher, I
would agree, but the heat gain to the space or heat loss (assuming the laws of
thermodynamics havent changed this week) would be slightly less as the
relationship between space temperature and inside surface temperature would be
decreased.</FONT> Also, infiltration/exfiltration losses are
typically<BR>through cracks. If the cracks in the interior surfaces are
warmer from<BR>radiant heating, then the crack warms the exfiltrating air, and
space<BR>temperature is not a valid criterion for calculating exfiltration
loss. So<BR>does a radiant heating system REALLY save any
energy?<BR><BR>3. If the radiant elements are imbedded in the ceiling,
which is common,<BR>the interior ceiling temperature can now be in excess of
90F, which<BR>increases the conduction losses to the attic. So if this
loss is counted as<BR>a delivery loss, the efficiency of the system drops
compared to the<BR>theoretical. The same argument applies to radiant
elements in floors. So<BR>is a radiant system REALLY any more efficient
than a convective system in<BR>terms of delivered energy?<BR><BR>4. With a
setback thermostat and a convective heating system, I can turn<BR>off the heat
at night, but my home will be comfortable in less than a 1/2<BR>hour the next
morning. But most radiant heating systems have a slow<BR>response
time. Do people turn them off/down at night, or do they run
them<BR>continuously?<BR><BR>----- Original Message -----<BR>From: "Jon Maxwell"
<jmaxwell@aspensys.com><BR>To: <bldg-sim@gard.com><BR>Sent: Monday,
April 12, 2004 8:46 PM<BR>Subject: [bldg-sim] Radiant
Heating/Cooling<BR><BR><BR>> I have modeled the savings for radiant systems
for unvented low intensity<BR>> gas fired radiant tube heating systems in
high bay warehouses and<BR>> manufacturing facilities in particular
by:<BR>><BR>> 1. Reducing the setpoint dry bulb
temperature a few degrees because<BR>> human comfort with radiant heating is
reached at a lower ambient than with<BR>> convection heating systems. I
am certain that comfort research supports<BR>>
this.<BR>> 2. Reducing the setpoint temperature a few
more degrees because there<BR>is<BR>> less floor-to-ceiling temperature
stratification. With the desired<BR>> temperature at belly button level,
radiant systems will have a lower<BR>average<BR>> temperature
floor-to-ceiling than unit heaters overall.<BR>> 3.
Reducing the amount of infiltration, due to reduced stack effect,<BR>due<BR>>
to reduced temperature stratification<BR>> 4.
Increasing the heating system combustion efficiency slightly due to<BR>>
having no intermediate media such as air or water between the
combustion<BR>air<BR>> and the space to be heated and lack of
venting.<BR>><BR>> While I cannot cite studies to validate the adjustments
or quantify them<BR>> generally (though I have rules of thumb based on
ceiling height), such an<BR>> approach has predicted savings roughly in the
right ballpark, close enough<BR>> to make a do/don't do decision at
least.<BR>><BR>> Would love to be able to cite rigorous research that
proves or disproves<BR>my<BR>> approach.<BR>><BR>> Jonathan B. Maxwell,
PE<BR>> Senior Engineer<BR>> Aspen Systems Corporation<BR>> 710 Park
Place<BR>> College Station, TX 77840<BR>> (979) 764-6779 wk<BR>> (979)
764-7810 fax<BR>> (979) 575-1281 mobile<BR>> jmaxwell@aspensys.com<BR>>
www.OPUSPOWER.com<BR>> www.aspensys.com<BR>><BR>> ----- Original
Message -----<BR>> From: "Chris Jones" <cj@cr-jay.ca><BR>> To:
<BLDG-SIM@gard.com><BR>> Sent: Monday, April 12, 2004 6:25 AM<BR>>
Subject: [BLDG-SIM] Radiant Heating/Cooling<BR>><BR>><BR>> In your
research with radiant heating cooling savings, have you found any<BR>> energy
"savings" that can be attributed directly to the use of the radiant<BR>>
system vs other systems (air supply in particular). For example, I
have<BR>> seen some papers that note that the heating setpoint can be relaxed
while<BR>> still maintaining thermal comfort with a radiant
system.<BR>><BR>><BR>> At 10:47 07/04/2004, you wrote:<BR>> >Dear
All,<BR>> ><BR>> >For those interested in the simulation of radiant
heating/cooling<BR>systems,<BR>> >IRC has developed a semi-analytical
model for integration in energy<BR>> >simulation software that use the
one-dimensional numerical modeling to<BR>> >calculate the heat transfer
within the building construction assemblies.<BR>> ><BR>> >The model
combines the one-dimensional model of the energy simulation<BR>> >software
with a two-dimensional analytical model. The advantage of this<BR>>
>model over the one-dimensional one is that it accurately predict the<BR>>
contact<BR>> >surface temperature of the circuit-tubing and the adjacent
medium,<BR>required<BR>> >to compute the boiler/chiller power, and the
minimum and maximum<BR>> >ceiling/floor temperatures, required for local
moisture condensation<BR>> >(ceiling cooling systems), thermal discomfort
(heating floor systems) and<BR>> >controls. The model predictions
for slab-on-grade heating systems<BR>compared<BR>> >very well with the
results from a full two-dimensional numerical model.<BR>> ><BR>>
>The model was implemented in the Canadian software HOT3000 and the
UK<BR>> >software ESP-r as a plant component. The implementation of this
model in<BR>> the<BR>> >ESP-r program offers additional flexibilities
to the radiant system<BR>> designer<BR>> >community, mainly:<BR>>
>· Designers can use any control
algorithm possible in ESP-r with<BR>the<BR>> >new plant component (e.g..,
use the flux or temperature control, and<BR>> compare<BR>> >their
performance).<BR>> >· Designers can
specify any number of radiant surfaces of the<BR>> building<BR>> >fed
by the same or different heat source.<BR>>
>· Designers can size realistic radiant
systems, and get realistic<BR>> >energy consumption (from the source side)
and cost.<BR>> ><BR>> ><BR>> >A copy may be downloaded
from:<BR>> >Laouadi, A. "Development of a radiant heating and cooling
model for<BR>> building<BR>> >energy simulation software," Building and
Environment, 39, (4), April,<BR>pp.<BR>> >421-431, Apr, 2004<BR>>
>(NRCC-46099)<BR>> ><<A
href="http://irc.nrc-cnrc.gc.ca/fulltext/nrcc46099/"
target=_blank>http://irc.nrc-cnrc.gc.ca/fulltext/nrcc46099/</A>><BR>>
><BR>> ><BR>> >Thanks<BR>> ><BR>> >Dr. Abdelaziz
(Aziz) Laouadi<BR>> >Research Officer<BR>> >Indoor Environment
Research Program<BR>> >Institute for Research in Construction<BR>>
>National Research Council of Canada<BR>> >1200 Montreal Road, Building
M-24<BR>> >Ottawa, Ontario, Canada, K1A 0R6<BR>> >Tel.: (613)
990 6868; Fax: (613) 954 3733<BR>> >Email:
Aziz.Laouadi@nrc-cnrc.gc.ca<BR>> >Web: <A
href="http://irc.nrc-cnrc.gc.ca/ie/light/skyvision/"
target=_blank>http://irc.nrc-cnrc.gc.ca/ie/light/skyvision/</A><BR>>
><BR>> ><BR>> >You received this e-mail because you are
subscribed<BR>> >to the BLDG-SIM@GARD.COM mailing list. To
unsubscribe<BR>> >from this mailing list send a blank message to<BR>>
>BLDG-SIM-UNSUBSCRIBE@GARD.COM<BR>><BR>><BR>> Chris Jones,
P.Eng.<BR>> 14 Oneida Avenue<BR>> Toronto, ON M5J2E3<BR>> Tel. 416
203-7465<BR>> Fax. 416 946-1005<BR>><BR>>
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