MRT Tool

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Is anyone aware of a simple Mean Radiant Temperature calculation tool? I'm
looking for something that will calculate MRT for a basic rectangular room.



No Username provide's picture
Joined: 2011-09-30
Reputation: 200


The ASHRAE-55 Thermal Comfort Tool created by the UC Berkeley Center for
the Built Environment and available from ASHRAE publications (if I
recall correctly) includes a very easy-to-use MRT calculator for
rectangular rooms. It allows for MRT at a particular position in that
room, separate surface temperatures and dimensions for surfaces, and
also the inclusion of a "panel" or other area within one of the walls
(such as a cold/hot window, heating panel, etc.) that has a distinct
temperature. This is part of a very handy tool for determining PPD, etc.
based upon the typical range of human thermal comfort variables (clo
value, activity level, air temp, MRT, humidity, air movement).


Timothy Moore

Timothy Moore2's picture
Joined: 2011-10-02
Reputation: 200

EnergyPlus also calculates and reports MRT and comfort outputs. I
haven't used the other tool, so I can't offer a comparison - just
another option.


Field, Kristin's picture
Joined: 2011-10-02
Reputation: 0

I do not think the thermal comfort tool calculates the MRT it is a user

Peter Simmonds. Ph.D.

Peter Simmonds's picture
Joined: 2011-10-02
Reputation: 0

It's an interesting conundrum that the times that MRT becomes a
significant player in the comfort calculation is when there is an uneven
radiant field (hot or cold window; fireplace; thermal mass wall). In
such a situation, is it fair to average out the MRT for an entire room?
Don't your view factors change drastically depending on your position in
the room?

Does one person too hot near the window and another person too cold on
the inside equal thermal comfort?

Vikram Sami, LEED AP

Vikram Sami's picture
Joined: 2011-09-30
Reputation: 0

Vikram, of course those two people even things out!! Umm, but really, this
is why I'm looking for a MRT calculator. This way I can test a few
locations in a given room quickly (much easier than doing hand calcs). I
think that used to have one online, but the
site seems to be down. Does anyone have any information? Is this site down
permanently, or is this a temporary issue?

I will probably end up with the ASHRAE calculator as it seems easiest to

Thanks for all the input.


No Username provide's picture
Joined: 2011-09-30
Reputation: 200

Ah, another can of worms. MRT is probably the least understood and
certainly the least calculated of space thermodynamics. ASHRAE RP 1383
was specifically set up to calculate MRT for spaces, even having unusual
configurations. It should be ready in about 18 months or so?

So Vikram, with reference to your analogy, how about this one?

Imagine a space that is naturally ventilated through an open window, at
this certain time of the day the occupant is in such a position that the
suns rays reach the occupant through the open window. What would the MRT
be in the space and how would this affect the occupants comfort.

Peter Simmonds. Ph.D.

Peter Simmonds's picture
Joined: 2011-10-02
Reputation: 0

ESP-r has a module that can calculate the view factor in any position
in the room. If you have the geometry in ESP-r, then you can specify a
location anywhere in the space, and the module will calculate the view
factor at that particular location.

I really miss that module when I work in EnergyPlus.



Ery Djunaedy's picture
Joined: 2011-09-30
Reputation: 0

JRR wrote;

Good Point !! Do you take the radiation temperature at the virtual
surface of the open window ??
NO. It is the wrong answer, but now you need to know things like the RT
of an adjacent building,
background sky RT, luminosity...

JRR's picture
Joined: 2011-10-01
Reputation: 0

The ASHRAE Standard-55 Comfort Model (proper name) does allow for a
single user input. However, immediately to the right of the MRT value,
it also includes a "Calc" button that opens a separate dialog. In this
separate dialog, the user can enter values for the following parameters:

Room dimensions

Occupant location

Occupant orientation (facing wall or azimuth)

Occupant position (seated or standing)

Temperature for each of four walls, ceiling, and floor

And dimensions, location, and temperature for a "window or panel" area
within each of the four walls, ceiling, and floor.

I just sent a post with the actual MRT calculation dialog box (for those
of you that receive visuals in your emails); however, it appears that
the screen shot of the dialog was too big for the Bldg-Sim list serve.

The IES Virtual Environment also provides MRT, dry resultant
temperature, and the full range of ASHRAE 55 thermal comfort input
parameters and results (PPD, PMV, etc.) for a location in the center of
the room, as well as surface temperature results for each individual
surface in the model. These surface temperatures, for any given
simulation time step, can then be readily entered into the ASHRAE
Standard-55 Comfort Model above if one is interested in thermal comfort
for a specific location within a rectangular room.

Timothy Moore

Timothy Moore2's picture
Joined: 2011-10-02
Reputation: 200

Regarding asymmetrical thermal comfort and that involving transmitted
short-wave radiation, the following link will get you an excellent
(lengthy, detailed, and very helpful) paper on thermal comfort in
proximity to windows. It discusses the effects of glass surface
temperatures and transmission properties, along with possible options
for including a rating of thermal comfort performance on NFRC window

Huizenga, C., H. Zhang, P. Mattelaer, T. Yu, E. Arens, and P. Lyons,
2006. Window Performance for Human Thermal Comfort
. Final Report to the National Fenestration Rating Council, Center
for the Built Environment, University of California, Berkeley, February.

You do not need an open window to have comfort issues associated with
transmitted short-wave radiation, nor does it have to be direct-beam
radiation-any window permitting occupants to receive a good dose of
transmitted diffuse and/or direct solar radiation is reason enough to
care about this effect. The paper at the CBE link above provides a very
useful means of estimating the contribution of both direct-beam and
diffuse solar radiation. The discussion of the impact of diffuse
radiation begins on page 44 and the discussion of direct radiation
starts on page 49.

CBE's Advanced Thermal Comfort Model

This tool can used to study the effectiveness of energy saving design
strategies, such as facade designs and advanced HVAC systems, in terms
of occupant comfort.

In addition, the CBE has an Advanced Thermal Comfort model that they
will be happy to run for you as consultants to your project (and which
their industry partners also have direct access to) which takes into
account short-wave radiation striking a human subject, along with
numerous very detailed thermal comfort parameters. This tool was used
for several key sections of the paper linked above, so you can see
examples of the model and results there. Not only does this model
account for occupant attributes like body mass (along with the usual
comfort parameters), it actually models 16 different human body parts
and the constriction and dilation of blood vessels that accompanies
different thermo-physiological states. This model, which is not really
all that difficult to work with, has been used for CBE consulting to the
automotive industry and a in-house by handful of large A&E firms. If you
want to learn more, the following link takes you to the section of the
CBE web site describing this tool:


Timothy Moore

Timothy Moore2's picture
Joined: 2011-10-02
Reputation: 200

You may also be interested in the work reported in an ASHRAE paper that
appeared at the last Chicago meeting:

"Predicting Local Thermal Discomfort Adjacent to
Glazing (NY-08-053)
Simon J. Rees, Ph.D., Member, Kevin J. Lomas, Ph.D. and
Dusan Fiala, De Montfort University, Leicester, UK

In this work a multi-segment dynamic comfort model has
been employed that incorporates recently developed models
of local thermal comfort response. The work required the
development of simulation methods able to predict the detailed
long-wave and convective exchanges to the surrounding
space and the absorbed solar irradiation. This has been done
in an effi cient and generic manner so that parametric studies
of local comfort responses have been possible. Such studies
have been used to examine the relationships between local
discomfort and room and window temperatures as well as the
role solar irradiation and clothing may play in determining
satisfactory winter environmental conditions."

The main points to note are that the model uses a local rather than
global comfort model i.e. effects on particular body parts are
considered. Direct solar radiation and shading of particular body parts
are calculated. View factors for each body part are calculated for a
particular body position relative to the room rather than calculating
the MRT.


Simon Rees's picture
Joined: 2011-10-02
Reputation: 0

I assume that this MRT discussion is about residential buildings with no dedicated perimeter heating and cooling system to maintain the temperatures of the inside surfaces of exterior walls and windows near the space temperature; and the supply locations of heating and cooling systems are well away from envelope.
Modern office buildings, even in extreme hot and cold climates, tend to be 70% glass today because of the low first, construction, and maintenance costs and also because they create a pleasant indoor environment. Today's glass efficiency is such that both heating and cooling systems of the perimeter zone (1' to 3") is by supplying conditioned air from the ceiling. Baseboard radiation, even in Minneapolis where temperatures drop to -30F, is not necessary. This frees up prime living space right up to the envelope without obstructions by HVAC units on the floor. The effect of solar radiation through the glass on MRT comfort inside is dealt with blinds. If the systems serving the perimeter fail, then the occupants have to leave the building since the windows are fixed shut to maintain inside pressure for fire and smoke control. MRT is not a factor inside these buildings if the Std90 Wall and Roof U-factors apply and the glass U-factor is about 0.3.
I have had to look at the MRT conditions inside such buildings in order to determine how inefficient the envelope could be made and still maintain comfort conditions inside based on MRT. This is a trial and error or iterative effort. In DOE2.1E you can get hourly report for EXTERIOR-WALL, Variable List Number = 6 (outside surface temperature). This information is not available for windows so an approximate value for outside surface temperature is the outdoor temperature assuming the glass outside surface is light-colored, smooth and low-heat absorbing. Transfer this information to an Excel file and calculate inside surface temperatures and MRTs at different distance. Surface temperatures of Space interior wall are assumed to be the Space design temperature. Some programming is required and extreme theoretical accuracy is not required.

Varkie Thomas's picture
Joined: 2011-09-30
Reputation: 0

My apologies... I've just learned that I in fact have a more advanced version of the ASHRAE Standard-55 Comfort Model than has yet been approved and published by ASHRAE, and the current published version does not include the MRT calculation tool.

ASHRAE is due to provide an updated version of the tool in the near future, but the timing of that is presently unknown.

The current release of the IES Virtual Environment does, however, provide air temp, individual surface temperatures, MRT, dry resultant temp, DPT, moisture content, and RH for all simulation reporting intervals. These results from the dynamic thermal model, plus user inputs for occupant clothing level, activity level, and local air speed then provide occupant PPD, PMV, and Comfort Index for each simulation reporting interval. To assess comfort in close proximity to a glazed fa?ade vs. the middle of a larger space, users can sub-divide the space to create a smaller thermal zone adjacent to the fa?ade in question.

Additional consideration are required to model the effects of transmitted short-wave radiation actually striking an occupant (see my prior post on this thread regarding asymmetrical thermal comfort involving transmitted short-wave radiation).

Timothy Moore

Timothy Moore2's picture
Joined: 2011-10-02
Reputation: 200


? Does one person too hot near the window and another person too cold
on the inside equal thermal comfort ?

The danger with an ?averaged? parameter is the assumption that one single
parameter can measure the comfort properties of a room - yet alone for a
whole building ? The daylighting people are trying to develop an
alternative to the ?daylight factor? ? they face the same issues. We
probably need an annualised colour-coded plan view of thermal comfort ( even
visual comfort ) for the floor space ?


Also see the book by Mark Bessoudo. It seems he wrote a book about his
thesis. He references the papers by Huizenga & Zhang

Building fa?ades and thermal comfort: The impacts of climate, solar shading,
and glazing on the indoor thermal environment

by Mark Bessoudo,

Below is a cut and paste from Amazon ? yada yada yada

Editorial Reviews

There is currently a trend of designing new commercial buildings with large
glazed fa?ades. Maintaining comfort in the perimeter zones of these
buildings is difficult due to their transmittance of solar radiation and
exposure to cold outdoor air temperature. Designing these buildings with
high-performance fa?ades, however, can improve energy performance, provide a
high-quality thermal and visual environment, and reduce thermal loads. This
book presents an experimental and simulation study of the indoor thermal
environment of a perimeter zone office with glass fa?ade and solar shading
device. The study investigates the impact of climate, glazing type, and
shading properties on thermal comfort. By considering comfort as a key
consideration in building design from the initial design stage through to
building occupancy, it can be ensured that new high-performance and passive
solar buildings are, not only aesthetically pleasing and energy-efficient,
but also comfortable and enjoyable places to work and live.

About the Author

Mark holds degrees in Biological/Environmental Engineering and Building
Engineering. He was a researcher with the Canadian Solar Buildings Research
Network and was awarded with the 2005 "Energy Ambassador" prize by the
Government of Canada. Mark is currently a green building consultant in

? Paperback: 248 pages

? Publisher: VDM Verlag Dr. M?ller (November 27, 2008)

? Language: English

? ISBN-10: 3639098242

? ISBN-13: 978-3639098242


Mike Barker

MikeBarker's picture
LEED EA Credit 1 Training
Joined: 2010-11-25
Reputation: 0

Hi all,

In E+, ASHRAE standard 90 (App. G) and in some other places, fan power for VAV systems with variable speed drives is modeled as a given function of part load ratio. I think the theory behind this originally comes from BLAST. This must be based on assumptions for the shape of the fan efficiency curve and on the pressure characteristic and control of the VAV system. Does anyone have access to the original theory on this? Alternatively, can anyone explain why and when the "single curve for all fans and systems" approach works?

Best regards,

Per Sahlin

Per Sahlin's picture
Joined: 2011-10-02
Reputation: 0

Dear Per Sahlin,

The simple fact is that fans which unload (those with variable inlet vanes ,
VSDs, etc.) do so in a way that is fairly represented by a curve. The
generic curves found in most energy analysis programs are reasonable
representations of the unloading characteristics. It is a good idea to have
a library of typical curves if your energy analysis program of choice
doesn't have such a library.

For a new building where your only purpose is to compare a "baseline" to
your specific design, it's reasonable to use a generic curve. This is
because the actual operating conditions are not known for new construction;
you know only the designer's best calculation, not the "as built"

For an existing building where you want to establish a model that represents
the actual conditions as closely as possible, it's probably worth developing
specific, custom curve coefficients for the installed fan(s).

James V. Dirkes II, P.E., LEED AP

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Joined: 2011-10-02
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