[Greenbuilding] Commercial Water Heaters
Paul Eldridge
paul.eldridge at ns.sympatico.ca
Mon Jul 16 19:56:29 CDT 2012
My firm just wrapped up a lighting retrofit at a local municipal
building where, as best as I can tell, there are four high capacity
electric water heaters. The two shown in this first picture
(http://i362.photobucket.com/albums/oo69/HereinHalifax/Img_1547.jpg)
each draw 36.0 kW and the remaining two (one of which is shown here:
http://i362.photobucket.com/albums/oo69/HereinHalifax/Img_1550.jpg) are
rated at 18.0 kW. Thus, the combined load of these four tanks is 108.0 kW.
These tanks are used almost exclusively for hand washing purposes, and
so we will be disconnecting all three top elements in the two 36.0 kW
tanks, as well as two of the three bottom elements, effectively
de-rating each tank to 6.0 kW. As you can see in the first photograph,
the two tanks feed a common supply, and 12.0 kW combined with almost
1,000 litres of storage capacity is more than sufficient to meet all of
their requirements. The two remaining tanks likewise serve mostly hand
washing needs and will be de-rated to 6.0 kW as well; with that, the
total connected load falls to 24.0 kW, for a net savings of 84.0 kW.
In terms of cost savings, an 84.0 kW reduction in coincident demand will
reduce our client's demand charges by $9,350.21 a year, i.e., 84.0 kW x
$9.276 per kW, per month x 12 months/year. It will also shift some
16,800 kWh of energy each month to Nova Scotia Power's lower cost second
tier, for an additional savings of $5,842.37 a year, i.e., 84.0 kW x 200
kWh/month, per kW x ($0.09904 - $0.07006 per kWh) x 12 months/year.
Taken together, this represents a savings of over $15,000.00 a year, at
current rates, achievable with no discernible loss in water heater
performance.
By simply reducing the power draw of these tanks, we will save our
client more money each year than by upgrading the facility's entire
lighting system, and will have done so at effectively zero cost (their
lighting retrofit will reduce coincident demand by an estimated 37.7 kW,
and de-rating their water heaters will more than triple that). Five to
ten minutes is all that's required to remove the jumper wires that
connect the terminal block to each corresponding heating element.
We've de-rated dozens of similarly oversized water heaters over the
years and in many cases implemented timer controls to lock-out their
operation during normal business hours, thereby reducing the customer's
peak demand even further; thankfully, there have been no complaints of
hot water run-out to date, and so the results have proven more than
satisfactory. This particular building initially served as a police
station, and so these water heaters originally feed a bank of showers;
the building was subsequently converted to general offices and,
consequently, their DHW usage is vastly lower.
The other thing we like to do is run the circulator pumps on
multi-program timers so that they operate only as required. For
example, we may run a circulator pump a couple hours at the start of
each weekday morning, shut it off, then turn it back on for an hour or
so mid-day and perhaps another hour later in the day. In most cases, we
can limit the operation of a pump to twenty or twenty-five hours a week,
as opposed to one hundred and sixty-eight; after all, there's really no
need to push hot water through an extensive network of pipes at 02h00 or
03h00 in the morning (with all the inherent losses), when the last
person had left the building eight hours prior.
BTW, you can view one of the rooms that we had upgraded at:
http://i362.photobucket.com/albums/oo69/HereinHalifax/Img_1546.jpg.
Here, we replaced 3-lamp F34T12 prismatic troffers that consumed
130-watts each with 2-lamp 28-watt 850 series T8 troffers that draw just
42-watts, for a two-thirds reduction in demand. Amazingly, light levels
in this area increased two and a half to three fold (originally, 14 to
17 foot candles, now 43 to 46 foot candles). Far more light and much
better light quality, with fewer watts to boot.
Cheers,
Paul
More information about the Greenbuilding
mailing list