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Mean Radiant Temperature (MRT) - Part IV
Copyright (c) 2011, Robert Bean, R.E.T., P.L.(Eng.) and
www.healthyheating.com
For additional
support visit our
visitor services page.
Mean Radiant Temperature (MRT) -
Part I: Introduction/theory
Mean Radiant Temperature (MRT) -
Part II: Application of
theory
Mean Radiant Temperature (MRT) -
Part III: Spreadsheet
tool for thermal bridging
Mean Radiant Temperature (MRT) -
Part IV: Project
examples & ASHRAE research
Mean Radiant Temperature (MRT) -
Part V: Calculation
example (REHVA GB #7)
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Mean radiant (MRT) and operative temperature
(Top) calculation
Below you will find screen shots from an Excel based MRT/Top calculation example using,
Figures 2.1, 2.2 and 2.4 from ''Babiak, J., Olesen, B.W., Petras,
D., REHVA Guidebook #7, Low temperature heating and high
temperature cooling, 2007"; and its comparison against the beta
test version of ASHRAE RP - 1383. This Excel
tool is not freely available as yet to our visitors but we do
give away a
thermal bridging tool for anyone wanting to evaluate net
insulation values in wood framed walls. Click the images below for an enlarged
view. |
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Figure 1. Using the REHVA example and formulas,
we have set up the office room geometry with dimensions for a
seated person located centrally in the room ignoring the facing
direction for simplification. |
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Figure 2. Shown is the tabular inputs and results
for each of the surfaces where the results are unity (equal to
one) Note the error is due to rounding. |
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Figure 3. Once the angle factors are established
they can be used as inputs into a surface temperature
calculation which then drives the mean radiant temperature (Tmr)
and operative temperature (Top)
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Software for modeling radiant effects on
thermal comfort
ASHRAE commissioned through research project 1383
to, "Develop
a Radiant System Module for the Simulation and Analysis of
Spaces and Systems". This software tool
can be used for evaluating the effects of radiant energy on
thermal comfort vis a vis the PMV/PPD
methodology developed by Fanger et al.
As of July 12th, 2012, the tool developed under
contract by Wrightsoft for ASHRAE, has been released to the T.C.
6.5 RP-1383 evaluating committee as a beta version. Using this
version we've taken the angle factor methodology defined
by
REHVA Guidebook #7 and developed the Excel tool illustrated
above, and compared it to the results from the RP-1383 software with
results being close or identical in some instances. We're
currently working to resolve any differences and will keep our
readers posted.
Ultimately the final version of the RP-1383 tool
will be available through ASHRAE and will incorporate the
ASHRAE Thermal Comfort Tool. If you
join our Linked-In group you get first hand notice of the
release or you could
become a member of ASHRAE and get access to the tool at
member price! In the meantime, below you find screen shots of
the input/output screens from the beta version of RP 1383, using the REHVA Guidebook #7
angle factor example. |
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Figure 4. The input/output screen shot (Beta test
version) for the REHVA room example showing angle factors,
emissivity and surface temperatures which were defined by our
Excel tool.
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Figure 5. The 3D fully rotatable output screen
shot (Beta test version) from ASHRAE RP-1383 illustrating the
MRT color contours at the seated level (0.6m). The 3D tool can
also illustrate PMV/PPD as per
ANSI/ASHRAE Standard 55 - Thermal Environmental Conditions for
Human occupancy.
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Figure 6. The PMV/PPD results (Beta test version)
for the Excel model and indication of compliance. As noted this
is a screen shot from the pre-release version. ASHRAE members
will be notified via press release when the tool is available
through the bookstore. |
For more on this topic read
operative temperature.
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Suggested reading:
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Karlsson, H.,
Modelling of Long Wave Radiation Exchange in Enclosures with
Building Integrated Heating, Chalmers University of
Technology, Dep. of Civil and Environmental Engineering,
Sweden, 2005
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Fanger, P.O.,
Thermal Comfort: analysis and applications in environmental
engineering, Danish Technical Press, Copenhagen, Denmark,
1970
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ASHRAE Research
Project 657. Simplified Method to factor Mean Radiant
Temperature (MRT) into Building and HVAC System Design
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