[Equest-users] Modelling Heated Windows in eQuest
Nicholas Caton
ncaton at catonenergy.com
Wed Jul 29 15:28:12 PDT 2015
A related elephant in the room: of the actual installed heating capacity
(i.e. “what’s drawn”), only a fraction of that heat will find its way into
the conditioned space. That figure is what you’ll want to use for the
baseboard heating capacity, if you do decide to go that route.
Some years back, the same topic of “active heating” windows came up with a
robust discussion thread. I’ve pasted what’s in my archive below for
reference. I’m not sure we came to any conclusive “best practice”
suggestions, but the discussion should prove helpful in determining your
own path forward!
You might want to consider foregoing the idea of any of this heat will
substantially contribute to the interior conditions. Put another way, you
may assume most heat will migrate to the colder side of the glass, that is
the exterior. Running with that and in lieu of using baseboards, you could
perhaps more simply set up this energy as a direct process or meter load
with an on/off/temp schedule.
~Nick
*NICK CATON, P.E.*
*Owner*
*Caton Energy Consulting*
306 N Ferrel
Olathe, KS 66061
office: 785.410.3317
www.catonenergy.com
*From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] *On
Behalf Of *bfountain at greensim.com
*Sent:* Wednesday, July 29, 2015 11:38 AM
*To:* 'Hari Jammulamadaka'; equest-users at lists.onebuilding.org
*Subject:* Re: [Equest-users] Modelling Heated Windows in eQuest
Baseboards are the only way I can think of to do it. The caution I have is
that DOE-2 uses baseboard heating first before any other heating to satisfy
zone heating requirements (including OA!). So, you would need to make sure
the window-baseboard heater capacity (which is not auto-sized) is
relatively small.
*From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org
<equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *John Aulbach
*Sent:* July-29-15 11:12 AM
*To:* Hari Jammulamadaka; equest-users at lists.onebuilding.org
*Subject:* Re: [Equest-users] Modelling Heated Windows in eQuest
Hari:
Could you possibly use Baseboard heating to simulate the heated windows?
Baseboards are usually under windows anyway to mitigate transmission loads.
Not sure how you measure the kBtu/kW of your windows, but you can translate
into the same heating capacity.
See if the offered eQuest controls for Baseboard satisfy your requirements
on the windows.
BASEBOARD-CTRL
Takes a code-word that specifies the control method for baseboard heating
in the zone. Defines the control method as THERMOSTATIC using HEAT-TEMP-SCH
as the setpoints, or OUTDOOR-RESET to allow BASEBOARD-SCH reset control.
This is a zone-level keyword for PLENUM-type zones; it allows "baseboards"
to be placed in plenums and allows the simulation of outside or space
temperature controlled heaters in the return air space. The plenum heater
is activated based on outside air temperature and reset schedule when it is
outside controlled. When it is space temperature controlled, and if the
interaction with the return air does not result in a temperature above the
scheduled value, the heater is turned on. In either case, the source of
energy input to the heater is defined by the specified or defaulted value
for BASEBOARD-SOURCE. See also BASEBOARD-CTRL, THROTTLING-RANGE and
BASEBOARD-RATING. Input for this keyword is the code-word that specifies
the method used for controlling the output of the baseboard heating element
in the zone.
THERMOSTATIC Baseboard heating is controlled by a thermostat
located in the zone. The program assumes that the baseboards add heat as
required, up to their maximum capacity, to maintain zone air temperature
within the heating throttling range.If there is a heating load the
baseboards are sequenced on first. If the baseboards cannot meet the entire
heating load, heating from the zone's air system, if available, will then
be activated.
OUTDOOR-RESET Baseboard heating is controlled by a thermostat
located outside the building. In this case the program assumes that the
baseboard heating output increases linearly as the outside air temperature
decreases. The linear function and the operating period are defined by
SYSTEM:BASEBOARD-SCH.
John R. Aulbach, PE
Los Angeles Ca
On Wednesday, July 29, 2015 6:49 AM, Hari Jammulamadaka <
hari.swarup at gmail.com> wrote:
Hello,
I am trying to model a building with heated windows (windows with heating
elements). The windows are not meant for comfort heating of the building.
Just localized heating for improving the comfort conditions in the
building. I have looked all over and couldn't find a way to model them. Can
someone suggest how I could go about this in eQuest?
Thank you.
Sincerely,
Hari
"Twenty years from now you will be more disappointed by the things that you
didn't do than by the ones you did do. So throw off the bowlines. Sail
away from the safe harbor. Catch the trade winds in your sails. Explore.
Dream. Discover." --Mark Twain
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*From:* Bruce Easterbrook [mailto:bruce5 at bellnet.ca]
*Sent:* Thursday, August 12, 2010 7:59 PM
*To:* Nick Caton
*Cc:* Namrata Vora; Sami, Vikram; Sam Mason; Bishop, Bill;
equest-users at lists.onebuilding.org
*Subject:* Re: [Equest-users] (no subject)
Nick you understand perfectly and Bill is the one you should be
listening to. This is what happens when marketing gets hold of something
without talking to engineering. It is all BS. I looked at both sites,
basically they are taking a low E thermopane and adding a third pane of
their heating glass. A real good 2 pane IGU will be about R-4.2, add
another pane and you could be in the R-7 range or a U value of .14, all
centre of glass. There is no way 2 pieces of glass in this 3 pane unit are
the same temperature. If the middle piece is almost the same temperature
as the warm inside piece that actually proves you have a huge amount of
heat moving to outside not to the inside. There will also be radiation,
and in this instance it will be significant as well. The reflective
properties of the low E glass will help, reflecting a certain percentage
back into the room as the glass should be throwing long wavelength
radiation but a significant portion will still flow through unless the low
E coat is thick enough, ie a mirror, which doesn't do much for looking
outside. Like you said earlier you have a radiator with a 70F room one
side and a winter night at -13F on the other side, it is not rocket science
to know in which direction most of the heat will flow.
Getting to the modelling using baseboards I don't think you can. A
baseboard is going to have a R-20 opaque surface behind it and the heated
glass is going to have a R-4 transparent surface behind it.
As far as I see it the only real benefit of this glass is you will be
able to run your humidity higher in the winter without having condensation
on the edges of the glass but at what I would estimate to be a significant
energy penalty. You would get most of these benefits just by having the
triple low E IGU with low conductivity spacers or by having curtains. You
will not heat a room with it and be able to pay the hydro bill. Note all
the conformances are for glass. I don't see any insulating window
certifications. Until these are tested no jurisdiction in NA will allow
you to use them with the numbers they are quoting.
Bruce Easterbrook P.Eng.
Abode Engineering
On 12/08/2010 06:50 PM, Nick Caton wrote:
Namrata,
I have patched Bill Bishop’s latest response in below in case you missed
it. He’s a proven smart cookie, and if he’s telling me I’ve got my head
wrapped around the problem the wrong way then I do believe him…
…but with that caveat, the manufacturer implying zero heat transfer through
the entire window assembly (because two of at least 4 surfaces have equal
temperature), sounds like flat-out misinformation to me. If two surfaces
of a material have equal temperature (say, 100 °F), then yeah, the
conduction between them would be zero, but that won’t prevent
convection/radiation from sweeping a majority of heat away when one side is
subject to sub-freezing temperatures! My car for example has a heated rear
window which helps me dislodge nightly glacier-formations in the
wintertime. On a cold day, the heat generated in that glass may help heat
the interior air somewhat, but surely a majority is going straight to the
literally frozen exterior, especially once the interior air has risen to a
temperature in which I can breathe regularly.
I remain skeptical of the concept of using heated windows as a good idea
for a space heating source (as opposed to a draft or condensation
mitigation strategy – perhaps to melt snow in a skylight as well?). Still,
if these units do put a significant fraction of heat into the space, I
think modeling electric baseboard heating will at the least be a good start
to emulate the space temperature behavior the actual system may help
achieve – though I’m still stuck wondering how you might account for the
amount of energy that is lost to the exterior as the units operate… hear
me out as I think my ducks are in a row here =)!
I’d be cautious that your manufacturer may be, intentionally or not,
dumbing down the discussion by framing their “effective U-value” as a
material property like “conductivity.” Conductivity is an arbitrary
material property that does not change with temperature – (i.e. steel has a
higher conductivity than air). U-values (and R-values) on the other hand
have that tricky little °F (or °C) in their units, because they are tied
directly to a heat transfer rate, which requires having a delta-T – in
other words, for a given set of material properties, the rate of heat
transfer is dependent on the difference in temperature the assembly is
subject to. That’s one reason we come across “summer” and “winter”
U-values for window assemblies.
It’s my intuition that eQuest (among other variables) uses the hourly
exterior temperature from the weather file alongside the hourly calculated
interior temperature for the parent zone to determine what temperature
difference to use when figuring the hourly heat loss through a window
assembly. A heated window however (when on) should be using a
fundamentally different figure for the interior surface temperature than,
say, 70°F when determining a temperature difference to find the hourly heat
loss for the zone.
I think I’m understanding now what we’re all getting at when we speak of
“effective U-values:” If a baseboard heating element in eQuest (or other
software) uniformly distributes 100% of its heat to the zone, then we might
account for the reality of a significant (?) fraction being lost straight
out the window by increasing the window’s effective U-value, in turn
modeling a realistically higher heat loss through the assembly on account
of the higher-than-normal heat temperature difference between the innermost
and outermost surfaces of the window, right?
I could certainly be wrong, but an approach defining an electric internal
equipment load with an custom equipment power curve (see Bill, below) *
*might** be easier than an approach defining dynamic window properties
(which I do not think is feasible in eQuest).
Again, I am not writing with full confidence that I completely understand
exactly how heated windows truly function, but critically thinking this
through is helping me get there! I look forward to anyone stepping up to
the plate to affirm or refute my current understanding =).
~Nick
[image: cid:489575314 at 22072009-0ABB]
*NICK CATON, E.I.T.*
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
*Check out our new web-site @ *www.smithboucher.com
*From:* Namrata Vora [mailto:namrata.vora at soladigm.com
<namrata.vora at soladigm.com>]
*Sent:* Thursday, August 12, 2010 2:08 PM
*To:* Nick Caton; Sami, Vikram; Sam Mason; Bishop, Bill;
equest-users at lists.onebuilding.org
*Subject:* active heating window modeling
All,
Thanks for your prompt responses
The mfg of this technology claim that since the temp difference b/n surface
3 & 4 is zero or minimal, there is no heat transfer out through the
windows. In addition the radiant nature of the heat allows the room
temperature to be set lower.
This particular company claims a u-value of 0.14 in non-heated state. I
tried creating such a low u-value dual pane IGU using WINDOW5 and was
unable to get that. So I created it directly in eQuest using simplified
glass type method. Now will try adding the radiant heating as electric
baseboard as suggested.
http://www.iqglass.com/products_iqglass/products_specs.html
I agree w/ Nick’s comment. In addition I wouldn’t think the window would be
in heating mode all the time. I would need to figure out when to trigger
the heating.
Namrata
Cell: 408-893-3729
*From:* Bishop, Bill [mailto:wbishop at pathfinder-ea.com
<wbishop at pathfinder-ea.com>]
*Sent:* Tuesday, August 10, 2010 1:36 PM
*To:* Nick Caton; equest-users at lists.onebuilding.org
*Subject:* RE: [Equest-users] (no subject)
Nick,
“The “efficiency” of these units … is going to vary hourly (probably
dramatically) based on the outside-to-interior temperature difference.” *Don’t
think of it as less heat to the space, but more heat to the exterior. The
window U-factor should take care of this.*
“apply an ON/OFF/TEMP schedule to an equipment or internal energy load?” *You
can apply an equipment power curve as a function of space temperature
(EQUIP-PWR-FT).*
*“*I’m concerned I might be missing something” *For the same glazing
properties, the heat loss to the exterior should be the same, EXCEPT that
the interior surface is now warmer, so radiative and convective losses
should be higher. Hopefully the manufacturers account for that in their
rated U-factor. I’m not convinced yet that there is any energy benefit to
this system.*
Regards,
Bill
------------------------------
*From:* Nick Caton [mailto:ncaton at smithboucher.com <ncaton at smithboucher.com>]
*Sent:* Tuesday, August 10, 2010 12:15 PM
*To:* Sami, Vikram; Sam Mason; Bishop, Bill; Namrata Vora;
equest-users at lists.onebuilding.org
*Subject:* RE: [Equest-users] (no subject)
On further thought, I think the equipment referenced would be
over-simplified if you just modeled an electric baseboard (that was my
intuitive reaction also – a few beat me to the punch)…
The “efficiency” of these units, meaning the btu/h delivered to the space
for every input kW, is going to vary hourly (probably dramatically) based
on the outside-to-interior temperature difference. If it’s -10F outside
and 70F inside, these are going to lose a ton of the input heat to the
exterior for the amount desired heat flowing inside – heat will flow
proportionately to where it’s coldest.
Time allowing, I’d propose achieving a much higher degree of modeled
accuracy by defining a series of equipment loads, each with *a custom
multiplier schedule* (even if the units in reality are under some kind of
thermostatic control) to account for when the units would be turned on.
This would be more work, but then you’re able to define a distinct sensible
HG ratio to account for the fraction of heat actually entering the space
(instead of lost to the exterior). As you can define up to 5 separate
equipment load/schedule combinations for one space, you could come up with
a weighted efficiency to apply to the SHG ratio for up to 5 different
blocks of time. Further explanation: This would involve creating hourly
reports to compare the hourly exterior temps to the target heating temp for
the interior, for the times the units would be operating, and to use that
info to figure out an hourly efficiency for the system based on how much
heat would actually find it’s way into the interior zone. Those hourly
results could be used to come up with weighted SHG ratio values for 5
blocks of time.
On a related note, I’ve got a question for everyone: Does anyone know of
any workaround (aside from extensive excel number-crunching) to apply an
ON/OFF/TEMP schedule to an equipment or internal energy load?
On another tangent, for my own education, am I wrong to consider heated
glass as an intrinsically *inefficient* approach to space heating? It
seems most appropriately applied as a “band-aid” or “patch” solution to a
decision to put too much glazing where drafts will cause discomfort. One
of the previous links has a claim: “When installed as part of a zone
heating strategy, heated windows can actually reduce the overall energy
consumption of a building by decreasing dependence on an inefficient HVAC
system.” Wouldn’t this need to be a *terribly* inefficient heating system
to compare unfavorably to a heating element losing >50% of its energy to
the exterior? I’m concerned I might be missing something fundamental for
HVAC design here… =/
~Nick
[image: cid:489575314 at 22072009-0ABB]
*NICK CATON, E.I.T.*
PROJECT ENGINEER
25501 west valley parkway
olathe ks 66061
direct 913 344.0036
fax 913 345.0617
*Check out our new web-site @ *www.smithboucher.com
*From:* equest-users-bounces at lists.onebuilding.org [
mailto:equest-users-bounces at lists.onebuilding.org
<equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *Sami, Vikram
*Sent:* Tuesday, August 10, 2010 11:07 AM
*To:* Sam Mason; Bishop, Bill; Namrata Vora;
equest-users at lists.onebuilding.org
*Subject:* Re: [Equest-users] (no subject)
I stand corrected – it is a good U-Value J
*Vikram Sami*, LEED AP
Sustainable Design Analyst
1382 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462 f: 404.892.5823 e: vikram.sami at perkinswill.com
www.perkinswill.com
*Perkins+Will.* Ideas + buildings that honor the broader goals of society
*From:* Sam Mason [mailto:sam.mason at atelierten.com
<sam.mason at atelierten.com>]
*Sent:* Tuesday, August 10, 2010 12:00 PM
*To:* Sami, Vikram; Bishop, Bill; Namrata Vora;
equest-users at lists.onebuilding.org
*Subject:* RE: [Equest-users] (no subject)
Vikram,
The conversion from W/sq.m.-K to Btu/hr-sq.ft.-F is 5.68. This gives a
U-value of 0.162 Btu/hr-sq.ft.-F.
I would like to see a study of the energy consumption of this window
compared to a building with normal low-e IGU and actual radiators.
Sam
--
Sam Mason
Atelier Ten
*From:* equest-users-bounces at lists.onebuilding.org [
mailto:equest-users-bounces at lists.onebuilding.org
<equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *Sami, Vikram
*Sent:* Tuesday, August 10, 2010 11:47 AM
*To:* Bishop, Bill; Namrata Vora; equest-users at lists.onebuilding.org
*Subject:* Re: [Equest-users] (no subject)
I’m a little curious – is 0.92 W/m2k a good U-value? Just poking around on
online converters – it looks like the IP version of that is around 0.56 or
something in that region – doesn’t seem spectacular (you get 0.25 with a
lot of double pane low-e IGUs). Unless the 0.922 is for the entire glazing
assembly – in which case its around the same as other glass types.
I might have got the conversion factor wrong.
*Vikram Sami*, LEED AP
Sustainable Design Analyst
1382 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462 f: 404.892.5823 e: vikram.sami at perkinswill.com
www.perkinswill.com
*Perkins+Will.* Ideas + buildings that honor the broader goals of society
*From:* equest-users-bounces at lists.onebuilding.org [
mailto:equest-users-bounces at lists.onebuilding.org
<equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *Bishop, Bill
*Sent:* Tuesday, August 10, 2010 11:25 AM
*To:* Namrata Vora; equest-users at lists.onebuilding.org
*Subject:* Re: [Equest-users] (no subject)
Namrata,
I would model the heating as electric baseboards and select a glazing type
based on the U-value and SHGC.
Regards,
Bill
*William Bishop, PE, BEMP, LEED® AP | Pathfinder Engineers & Architects LLP*
Mechanical Engineer
134 South Fitzhugh Street
Rochester, NY 14608
T: (585) 325-6004 Ext. 114
F: (585) 325-6005
wbishop at pathfinder-ea.com
www.pathfinder-ea.com
P Sustainability – less is more.
------------------------------
*From:* equest-users-bounces at lists.onebuilding.org [
mailto:equest-users-bounces at lists.onebuilding.org
<equest-users-bounces at lists.onebuilding.org>] *On Behalf Of *Namrata Vora
*Sent:* Tuesday, August 10, 2010 10:34 AM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] (no subject)
How does one model active heating windows like the ones listed below.
http://www.iqglass.co.uk/p/h/Products/U_Values_%26_Benefits/218/
http://www.thermiquetech.com/about_heated_glass.html
Namrata Vora
408-893-3729
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