Boiler oversize problem

Dave Heckman

Replaced at 40hp low pressure boiler with two 20hp units. The problem is that steam demand greatly decressed in the building, due to the installation of gas-fired single package rooftop units that provide much of the building comfort heat. In fact, one 20hp boiler seems to be too much for the location now, as the unit keeps cycling on and off causing numerous problems. Any recommendations that do not include boiler replacement would be greatly appreciated.

kevin coppinger_4

YOU MAY...

be able to downfire the boiler but don't count on it...most boiler mfg. frown upon this...tried it once. Call the factory...kpc

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Dave Heckman

frowning

thanks, i was just hoping someone might have had a miracle answer out there. some new add-on, conversion equipment, etc. that would prevent the replacement of fairly new boilers.

Steamhead

You could always

stop using the heating function of those rooftop units. Or find another heat-related application such as domestic hot water that the boiler could supply.

[Deleted User]

Downsizing

C/I sectional? If so, pull out a few sections & match a new burner to the smaller boiler. Some burners fit several boiler sizes. Reducing input on the right burner is relatively simple. New rating plate & away you go.

Brad White_2

Modulating fire?

Sounds too low in BHP for modulating fire but do you have or can you at least get lo-hi-lo control on the burner? Again, as Kevin suggests, only with manufacturer's blessing.

What is the cut-in/cut-out differential? Can the system tolerate wider swings?

Christian Egli

Agreed, get rid of the rooftop units...

It seems a 10 / 30 HP combination would have been more convenient than the 20 / 20 HP. What is it? Hindsight is 20/20

I have had experience with downsizing an 80 to 60. It required a lot of insisting. The result has been satisfactory.

Since then I have been thinking that a different control would solve a lot of your problems. Standard boiler systems work with a much too wide swing between on and off and that is probably the source of your hic-ups.

If you are inclined to doing so, look into control systems that are available for industrial furnaces. I have solved over-firing problems with a furnace by fiddling the controls only, by patiently adjusting PID settings. We achieved a very stable set point with no over shoot and no dips, plus the control ramps the heat up rather than turning it up in an instant.

I have always thought the same idea would benefit a boiler, it would follow the same idea behind modulating burners but without using the modulating valve.

What kind of burner do you have? What type of boiler is it? Water-tube, fire-tube, low water volume?