[Greenbuilding] Commercial Water Heaters

[Peter Kidd]

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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