[bldg-sim] Radiant heating modeling paper

[Laouadi, Aziz]

The realistic energy saving of radiant systems when compared to warm air
systems is not an easy task to conduct as it depends not only on the
physical characteristics of the building and HVAC system, but also on
occupant behavior vis-à-vis the control of the radiant system.  It is well
known that the main claim by radiant system designers and manufacturers is
that the energy saving may be achieved by lowering the thermostat set point
temperature.  However, recent research has showed that it is not the case
(see for example SOLPLAN REVIEW journal, March 2001): homeowners with
radiant heating systems do not set their thermostat temperature
significantly lower than homeowners with other type of heating systems.  In
addition people tend to like the surface warmth the radiant system create,
and therefore extending the heating season and the annual energy cost.

To get a realistic picture on the energy performance of radiant systems, an
integrated approach should be sought.  The integrated approach should
account for the heat transport from the heat source to the radiant surface,
from the radiant surface to the indoor air, from the indoor air to the
exterior environment, and the dynamic control of the radiant system.
Nowadays, energy simulation software offer this opportunity.  The radiant
model, which is the subject of this discussion, was specifically developed
for energy simulation software. The model handles in a detailed and dynamic
way (transient) the heat transfer from the heat source (e.g. boiler) to the
slab through tubing, and from tubing to the construction layers of the slab.
Other heat transfers,  including building heat loss from the indoor air to
the exterior, and the control of the radiant system are taken care by the
energy simulation software.  Combining of a detailed radiant heating/cooling
model with energy simulation software offers many features and design
flexibilities to the designer, namely: (1)- examine the dynamic behavior of
radiant systems (for example, nighttime setback temperature, or exterior
temperature variations, ON/OFF control, etc., and its impact on the response
time and energy consumption).  It should be noted that the current design of
radiant systems is based only on steady state behavior (e.g., ASHRAE
Standard 152). (2)- explore any possible control type on the energy
performance of radiant system.  For example, if the energy simulation
software provides calculation of thermal comfort indices (MRT temperature,
Operative temp., PMV, or PPD), then one may use these outputs to control the
radiant system, and double check the energy saving potential of radiant
systems upon lowering the set point temp. (3)- Design a radiant system for
specific building location, by taking into account the local weather data.
This just to name a few.

Reply to specific questions:

Q: Does the model have the capability of
simulating a variety of insulation approaches?  There is a great need for
information on when, where, and how much insulation to apply.

A: Yes it does. In fact there is no limit on the construction layers of the
radiant surface (e.g., flooring, back insulation, etc.) as long as it can be
handled by the energy simulation software.  However, peripheral (edge)
insulations are not accounted for in the model.  The model assumes the edges
of the radiant surface are adiabatic (well insulated).

Q: In your research with radiant heating cooling savings, have you found any

energy "savings" that can be attributed directly to the use of the radiant 
system vs other systems (air supply in particular).

A: I have not done myself any research on the comparison of radiant systems
with warm air systems.  However, there are some theoretical research that
claim that radiant systems save more energy than conventional ones.

Thanks  

Dr. Abdelaziz (Aziz) Laouadi
Research Officer
Indoor Environment Research Program
Institute for Research in Construction
National Research Council of Canada
1200 Montreal Road, Building M-24
Ottawa, Ontario, Canada, K1A 0R6
Tel.:  (613) 990 6868;	Fax:  (613) 954 3733
Email: Aziz.Laouadi at nrc-cnrc.gc.ca 
Web: http://irc.nrc-cnrc.gc.ca/ie/light/skyvision/


-----Original Message-----
From: David Springer [mailto:springer at davisenergy.com]
Sent: Monday, April 12, 2004 1:23 PM
To: aziz.laouadi at nrc-cnrc.gc.ca
Subject: Radiant heating modeling paper


Mr. Laouad,

I received and briefly reviewed your paper (I will take a more thorough look

when I have more time).  This is a topic that interests me greatly.  I have
some questions and observations.  Does the model have the capability of
simulating a variety of insulation approaches?  There is a great need for
information on when, where, and how much insulation to apply.  We are
planning to develop a  "slab edge insulation form" under work we are doing
under the Department of Energy 'Building America' program and will need to
estimate the benefits.  

It seems that output from your model could improve upon what is currently
included in ASHRAE Standard 152 (hydronic section prepared by John Andrews
and Birol Kilkis).  I believe it is inadequate to represent radiant floor
efficiency at the same level that the standard can be used to represent
duct efficiency.

I have several months of monitoring data from my own house that includes
both radiant heating and radiant cooling, if you are interested in using it
for model calibration.  Unfortunately the surface temperature measurement
is not very good.

I forwarded your paper to Larry Drake at the Radiant Panel Association.  I
am sure he will be interested in publishing a review in the monthly
association newsletter.

Dave Springer
Davis Energy Group

===========================
You received this e-mail because you are subscribed 
to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe 
from this mailing list send a blank message to 
BLDG-SIM-UNSUBSCRIBE at GARD.COM