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In the July and August issues of Professional Carwashing & Detailing®, I wrote about how I saved 26 percent on the cost of natural gas for the floor heat over the winter of 2005-2006 at my self-serve carwash. This month, I’ll cover the water-heating boiler and a system to save up to 16 percent.
We have a 12-bay carwash, or more accurately, two six-bay carwashes perpendicular to each other. Each is a complete wash within itself, sharing only the closed-circuit TV and security systems. It means we have two boilers for the floor systems and two for the water heating systems.
With the high price of natural gas, heating oil or whatever you may use, any cut in the therms you use to heat water will help today, but may be even more significant later.
Currently, our boiler for bays 1-6 is wired so the water-circulating pump runs 24/7 (bays 7-12 are wired the same, but use a different brand of boiler). The water circulates through the boiler to the hot water storage tank and back again.
The boiler will fire when the temperature of the water in the tank drops below the thermostat set point of 120 degrees. When the water reaches the set point, the boiler shuts down.
Because the pump remains on, residual heat is drawn out of the boiler as it cools off. The water still circulates around the system taking the hot water out of the tank through the cold boiler and back again. This process continually cools the water. Eventually, the water is cool enough to require the boiler to fire again. All that heat used to warm up all that water can be wasted.
When the carwash is busy and requires the hot water, the efficiency of the boiler is not bad. But when hot water is not required, such as during slow times or at night, the efficiency of the boiler drops significantly because the heated water is circulated back through the cold boiler in a continuous cycle that may last all night. In the winter it might last for several days and efficiency is way down.
We could wire the boiler circulating pump so it only comes on when the thermostat in the water tank calls for heat and fires the boiler. But then — there always seems to be a “but then” — we can’t draw that heat off a still-hot boiler since the pump is not running because the pump shuts down at the same time as the boiler. All that residual heat escapes through the boiler flue and is wasted.
The efficiency of the hot water boiler in this case is not very good either.
One reason I didn’t worry about the cost of heating the water was that I could see the return on investment because the customer is paying for it, less the efficiency.
Another reason was seeing a gas bill in the summer that was less than half the winter bill. I was so happy about not paying the high winter bills I was complacent about the summer bills.
But stop a moment and think. If the gas in the summer is used for only heating the water, (remember, there is a separate heating system for the floors) then the same amount of gas should be used in the winter for heating water too, if the business, winter-to-summer, is 50/50.
It isn’t really 50/50, but close enough for us — we’re not building a piano.
So, just under two-thirds of our natural gas use is for heating water. If we can save 16 percent on two-thirds of the gas bill, that’s a lot of quarters. You’ll have to do the math yourself.
Which case is better?
We have always run our circulating pumps 24/7, not necessarily because we thought it was more efficient, but because that was the way it was done at the time and we never really thought about it or worried about it.
The price of natural gas was below 50- cents a therm and we didn’t have a $2,500 monthly gas bill until the winter of 2004-2005. Now we’re faced with the high cost of gas and prospects for continued increases in the future, it’s time to think about it.
The answer to the question “Which case is better?” is, drum roll please: Both. Enter the Raypak Economaster II.
The Raypak Economaster II is for use with Raytherm, Hi Delta and ADB boilers.
It’s simple really. When the temperature of the water rises to the set point of the tank thermostat, the control voltage is interrupted but the circulating pump keeps running for up to 10 minutes after the thermostat is satisfied.
The actual run time can be adjusted from three minutes to 10 minutes. Larger boilers require longer run times to use all the residual heat from the heat exchanger.
Obviously, in my case the pump will run only until all the heat is drawn off the heat exchanger. And I get to adjust that time. I’ll set the time delay so the pump shuts off as soon as the boiler is cool to my hand.
The savings are in the energy to run the pump. The pump is usually a fractional horsepower pump and doesn’t consume a lot of energy but over time it does add up.
Also, there is the wear and tear on the pump to consider. The spider couplings will wear out faster because there are more starts and stops, but the motor and pump runs less.
In Case II, the savings will be that we use all the residual heat left in the boiler before it escapes up the flue.
With this system the boiler should fire less because during slow times when hot water is not being used, the only heat loss will be through the water storage tank walls which should be insulated.
That’s the basics on how the thing works. I’m not the real expert, though. You should get with your boiler guy for additional information.
Unfortunately, I cannot, at this time, report first-hand experience on how well this works because I have not installed it yet.
You are reading this in November, but I’m writing it in the middle of September. I still have time to get this system installed; right after I finish the other projects I’m working on, such as:
On a closely-related subject, if you’re building a new carwash or planning on replacing your hot water boiler, consider the new vertical condensing high-efficiency units. They are stainless steel, up to 99.8 percent efficient and zero clearance to combustibles.
I’m not sure about the cost of the units, but with a 99.8 percent efficiency rating, it shouldn’t take too long to pay for itself in fuel savings.