[Greenbuilding] Commercial Water Heaters

[Paul Eldridge]

Hi Peter,

It's hard for me to provide you with a proper answer; data loggers would 
certainly help us to determine this more accurately.

I can confirm that the heating system is natural gas, that there are no 
supplemental baseboard strips or in-duct re-heats, and that the average 
monthly peak is 318 kW.  Unfortunately, I don't know the seasonal 
variation, so I can't properly account for the air conditioning load.  
FWIW, we had pegged the original lighting load at 87.5 kW, so lighting, 
pre-retrofit, would account for just over one-quarter of the building's 
average electrical demand.

As previously noted, the two 36.0 kW tanks are ganged together, so 
there's a high probability that their operation will overlap at some 
point during the monthly billing cycle.  If I were to guess, coincident 
peak most likely occurs somewhere around the mid-day mark, and this 
would be presumably a period of higher hot water demand due to heavier 
use of the wash rooms and staff kitchens.  The other two satellite tanks 
serve kitchens as well, so it's not unreasonable to expect that they too 
would fire-up around the mid-day peak.

Cheers,
Paul

|great example of re-commissioning. that said, is the building
|electrically heated, and with that low a hot water demand, are they
|likely to see that reduction in coincident demand?

>/  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
/>


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