08-30-2011, 08:14 PM
I'm trying to convince management in some of our bigger, older buildings to upgrade our HVAC controls from pneumatic to DDC in all our mechanical rooms and VAV terminals but am being asked to estimate savings from such a project. Are there any commercial rules of thumb for projected energy savings from the added precision, more instanteneous response, reduced maintenance/calibration per sq ft or per climate etc?
I've calculated the air compressor savings with approximate load profiles which were surprisingly low (each is no more than 5HP). Seems like so much else requires massive assumptions on how poorly the building currently operates or is scheduled and how many problems will be fixed as the project is undertaken (ie stuck reheat valves discovered during pneumatic actuator replacement)
08-30-2011, 08:16 PM
Brian put your email in your profile and I'll contact you.
08-30-2011, 08:48 PM
Likely one good way to show justification would be to find documented savings from similar upgrades in similar buildings. Hopefully someone here could know of some examples.
The Command for the Air Force Base where I am currently working just approved a $700,000 project to upgrade the existing DDC controls for 30 buildings, based on similar justification (savings demonstrated in similar buildings).
08-31-2011, 11:07 PM
Energy savings from 10% to 30% are usual from a DDC install. Setpoint control (better Source-Load matching), reduction of simultaneious heating and cooling and scheduling gives you most of the bang, You can figure on laying off half the bldg. engineers too!
Its not a matter of IF it will payback, just how long. This is balanced against what other
nrg improvements could be made, envelope and primary equip. effiency improvements, and terminal device upgrades. in an old building sometimes other items that are obvious on the payback are choosen first.
I remember when we first started the ddc thing, was at powers, we put together a manual on Energy Management Guidelines which detailed calcluations for figuring savings based on some rough numbers. They were indexed by application, so you
had hw reset, chw reset, PID loop improvmnt, pead demand, duty cycling, economizer control, chiller plant optimization, cooling tower wb reset, etc..
one would pick what they wanted and add up the savings, it seem to always end up like a 70-90% reduction , or more than 100% lol,
More detailed calcs, involve using some 365 day simulation software, like the Trane Tracer or Carrier HAP programs. These allow you to change the type of air system for instance, vav or cv, type of source, heating and cooling, and setpoint adjustments that will give you the differences and annual savings.
"Seems like so much else requires massive assumptions on how poorly the building....."
you are right it is really not much more then a wag, but if you put together enough
pages in your report with lotsa refernces and complicated drawings, most will buy
into the concept. ;)
There may be other savings, personell productivity improvements, reduced health costs,
improved iaq, monitored critical systems that may have a high cost if failure occurs, and when they start charging for carbon a whole mess of other charges you may escape..
i have seen some studies that show more cost reduction from these items then from nrg ones.
A more comprehensive energy study done by a reputable firm would make more sense if this is an older building which hasn't been touched in a long time.. You'll need that kind of
documentation if you expect some funding for such an improvement that generally requires some entity to provide revenue.\
having said that,,
you could order up two or three control companies to come in and give you a price on one of the buildings, tell em ya need an estimated savings, ( say it can be rough ;))
and get the utility bills for the last 3 years..
use the average of the savings that they gave you..
and multiply it by the utility costs (adjusted )
figure on nrg going up 100% over the next five years,
and you got your simple payback,
its usually needs to be 2, and sometimes less,
this is all just generalized talk, your results may differ!, but the question of
how much will it save?
to me has become a somewhat mute point as there are so many instances of
succesful application of digital controls and with hugely escalating nrg costs,
that its more of a question,
how long can we wait before we have to do it?
because we can't afford not to.
and thats ok, cause a lot of management ppls think that way about everything ;)
btw,use the big valve operators, keep em pneumatic..
they're expensive ;)
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