[Equest-users] LED Lights (UNCLASSIFIED)

[Nick Caton]

John et al:

 

The query seems to be branching out pretty quickly ...  I have many
thoughts on the broader topic and present state of LED's and their that
wouldn't make everyone happy to read/hear, but I think this addresses
the heart of John's post directly:

 

The problem of lights as an internal heat load remains pretty simple for
us energy modelers and HVAC designers, and isn't made more difficult by
LED technology.  

 

Consider a light fixture of any source as the boundaries of a
thermodynamic problem:  Energy in = Energy out.  If we put 100W of
energy into the fixture, then 100W of energy must be produced in some
form.  That output is some combination of visible light energy that our
eyeballs can perceive, and invisible other energy which can largely be
perceived as heat/sound after transmitting through the air or other
surfaces to arrive our eardrums/skin.  Normally that ratio of output
visible light energy is tiny, but for certain LED sources it's less
tiny**.  That fraction is entirely moot however from an building energy
simulation standpoint.  All energy output in the form of light will
encounter surfaces (floors/walls/people) and ultimately be absorbed*.
In the process, the energy will briefly excite a few electrons... but
when the lights go off and the excited electron-party is over all that's
left is energy irradiated an invisible wavelengths (excepting
glow-in-the-dark t-shirts).  The big point here is, energy input is the
only figure/variable we really care about, because that's exactly the
amount of energy we need to consider from an HVAC heating/cooling
perspective.  None of it just goes away.  

 

~Nick

 

* Acknowledging:  A fraction of light hitting exterior windows transmits
out of a building - I'll claim this negligible since that's a fraction
(glass transmittance) of a fraction (window to every-other-surface
ratio) of an already small fraction of the input watts (visible light
vs. other wavelengths).

 

** If anyone cares to better understand this careful choice of words, or
wishes to better cut through marketing mis-information from the lighting
industry, I would first advise taking some time to review difference in
the terms 'efficacy' & 'efficiency,' then identify the contextual
mis-use in the preceding discussion below.  Incorrect conclusions
regarding heat are made as a result.  A hint:  Both can use units of
"lumens per watt" in the right context,  but lumens per watt of light
output is not the same thing as lumen of light output per watt of input
energy  ;).

 

 

 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Charles
Holleran
Sent: Friday, October 07, 2011 10:49 AM
To: john.s.eurek at usace.army.mil; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] LED Lights (UNCLASSIFIED)

 

LED's use DC power, and do so efficiently.  Sounds like you're referring
to the AC-to-DC power supply though, not the LED light source itself.
 
As described in your post below ACDC power converters can be loosely
lumped into 2 categories:
- old, inefficient, big, hot, LINEAR converters with their big
transformers, and
- newer smaller, cooler, SWITCHING converters ("the cool kind" referred
to below)
 
I think Enerstar has done a lot to phase out the inefficient LINEAR
converters.  You can still procure the LINEAR power supplies.  But you
probably won't find one that meets Enerstar requirements.  The SWITCHING
supplies are much more efficient, and may even cost less now, as they
are smaller, lighter, and have less metal in them.
 
So here's a couple of Enerstar links for some reference material:
http://www.energystar.gov/index.cfm?c=archives.power_supplies
http://www.energystar.gov/ia/partners/product_specs/program_reqs/eps_pro
g_req.pdf
 
For more information on SWITCHING ac to dc supplies:
http://en.wikipedia.org/wiki/Power_supply#AC.2FDC_supply
 
The Wiki article gives some ideas as to the "magic" that is achieved
with the new supplies.
 
If the question was about the LED's themselves and not the
transformers/converters that go with them then please excuse my
sidetrack.
 
If anyone has seen central DC converters wired throughout the facility
I'd be very interested to hear about it.  Certainly many loads are now
DC.  Perhaps the Tesla Wars (
http://en.wikipedia.org/wiki/War_of_Currents) are swinging back towards
Edison for efficiency reasons.
 
Charlie Holleran
Holleran Technologies
scorpdaddy at hotmail.com
 

 

> Date: Fri, 7 Oct 2011 09:27:55 -0500
> From: John.S.Eurek at usace.army.mil
> To: equest-users at lists.onebuilding.org
> Subject: [Equest-users] LED Lights (UNCLASSIFIED)
> 
> Classification: UNCLASSIFIED
> Caveats: NONE
> 
> All,
> 
> Are LED lights really magical? We have all used a laptop and felt the
AC/DC
> converter get hot. We know that if a transformers (not the cool kind)
are
> inside a building they put off a lot of heat. What about the
transformers
> for the LED lights?
> 
> LED lights need DC power, where are all the transformers and were does
that
> heat go?
> 
> I suspect the LED light is like the electric car. It is cool that the
car
> runs off of electricity, just don't look at the coal that is burnt to
make
> the electricity. Yes LED lights give off almost no heat, but what
about the
> transformer?
> 
> Anybody have any information on this? What is the heat of rejection
from the
> transformers.... (I have done a little research and one solution was
to have
> a single transformer for the building and wire the lighting of the
building
> with DC power. Talk about changing business as usual.)
> 
> 
> John Eurek 
> 
> -----Original Message-----
> From: equest-users-bounces at lists.onebuilding.org
> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of John
Bixler
> Sent: Thursday, October 06, 2011 8:25 AM
> To: Taylor Sharpe; equest-users at lists.onebuilding.org
> Subject: Re: [Equest-users] Lighting densities and Electricalequipment
> contributing to Space Heating
> 
> Taylor,
> 
> 
> 
> A number of things play into the question you are asking.
> 
> 
> 
> * Different types of lighting have different efficiencies.
> Incandescent lights create a lot of heat, LEDs create practically no
heat.
> Fluorescent is somewhere in between but create much less heat then
> incandescent
> 
> * The style of light installed - is it pendant hung in the space? If
> so, 100% of the created heat is given to the space. Is it recessed? If
so,
> a portion of the heat is given to the plenum, and some of the heat
given to
> the plenum leaves the building as relief air (in fact, it's possible
that all
> the plenum heat leaves the building in the case of a 100% outdoor air
system)
> 
> * The schedule of the lights. Were you looking at yearly consumption
> or peak heating load? Peak heating load is typically calculated with
the
> lights (and occupancy and misc loads) at 0%. If you were looking at
yearly
> consumption, but your modeled facility has the lights turned off for a
> majority of the time, the impact may be minimized.
> 
> 
> 
> Point being, you have to consider more than just lighting density when
you
> make this analysis. 
> 
> 
> 
> John Bixler, EIT, LEED AP BD+C
> 
> Mechanical Designer
> 
> Sebesta Blomberg 
> sebesta.com | P 319.364.1005 | M 319.558.9299 
> 
> 
> 
> This message has been sent via the Internet. Internet communications
are not
> secure against interception or modification. Sebesta Blomberg
therefore can
> not guarantee that this message has not been modified in transit. This
> message and any files transmitted with it are confidential and
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> 
> 
> 
> 
> 
> 
> From: equest-users-bounces at lists.onebuilding.org
> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of
Taylor
> Sharpe
> Sent: Wednesday, October 05, 2011 10:18 PM
> To: John Bixler
> Subject: [Equest-users] Lighting densities and Electrical equipment
> contributing to Space Heating
> 
> 
> 
> Hi everyone,
> 
> I feel that this topic must have been discussed at some point, but an
> exhaustive archive search got me nowhere, so I thought I'd throw
together a
> post of my own, especially since I'm working on an eQuest model of a
small
> server building which is heated in part by a large number of computers
that
> run many hours every day.
> 
> I'm interested in how eQuest treats electric loads - from lights,
computers,
> refrigerators, etc - as regards space heating. I had always assumed
that,
> especially in the case of lights, much of the energy used would be
converted
> to heat within the building, and contribute to space heating.
> 
> However, I set up an experiment to test this and found that the
results were
> far different from what I'd expected: I upped the lighting density in
an
> existing natural-gas-heated building model by about 15x and compared
the
> electric use from before and after the lights were increased. I
converted
> all values to mmBtus for easy comparison. To my surprise, I found that
only
> a very small fraction (about 6%) of the mmBtus added to the building
through
> those lights contributed to space heat. The kWh recorded were
increased
> hugely, but the heating energy required to keep the building heated
was
> almost the same in both cases.
> 
> I repeated the experiment, upping misc. equipment instead of lighting,
and
> saw a similar result.
> 
> Does anyone have any knowledge of what equations eQuest uses to decide
how
> much electrical energy use is converted to heat and added to the space
in
> which it is installed?
> 
> Regards,
> Taylor Sharpe
> Sharpe Energy Solutions
> newspectrum at gmail.com
> (541-840-5698)
> 
> 
> Classification: UNCLASSIFIED
> Caveats: NONE
> 
> 
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