Quickly need article(s) extolling virtues of MBS......JohnNY

Robert O'Brien

http://www.weil-mclain.com/consumers/products_static/mult_boiler.html

<A HREF="http://www.heatinghelp.com/getListed.cfm?id=313&Step=30">To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"</A>

JohnNY

That's Multiple Boiler System.

I'm looking at a great opportunity to build some much-needed efficiency into an old system.
Trying to take a "don't take MY word for it" approach to the sale.

Any help greatly appreciated.



To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

JohnNY

Thanks, Robert!

Outstanding article and I'm including it in my proposal, but I was hoping for non-manufacturer input, too.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Robert O'Brien

John

This is from an article by Siggy.The whole thing is available at http://www.esmagazine.com/CDA/Archives/5837193d0bda8010VgnVCM100000f932a8c0____

Multiple boiler systems have been around for several decades. The underlying concept is simple: Divide the overall heating load among two or more independently controlled boilers, and operate only the boiler(s) necessary to meet the load at a given time. Each boiler constitutes a “stage” of heat input. An intelligent controller continually monitors system supply temperature and determines what boiler stages to operate to keep that temperature at or very close to a target temperature.

The benefits offered by multiple boiler systems include:

* Increased seasonal efficiency relative to that of a single large boiler.
* Partial heat delivery if one boiler is down for servicing. This is especially important in locations where extreme temperatures could quickly freeze up nonoperational systems.
* Easier installation than with a single larger unit, especially on retrofit jobs. Repair parts are often more readily available for smaller boilers.
* The ability to provide elevated output during periods of high domestic hot water demand or snow melting, while still retaining high efficiency under lower space heating loads.

Figure 1 shows the operating characteristics of two different multiple boiler systems relative to a hypothetical load profile. The first system uses two on/off boiler stages, each capable of supplying 50% of the design load. The other has four on/off boiler stages, each capable of supplying 25% of design load. Notice how the four-boiler system is better able to track the load profile relative to a two-boiler system.

Based on this, one might conclude that the more stages the boiler system has the better its ability to match the heating load, especially under very low load requirements. However, as the number of boiler stages increases so does the ratio of boiler jacket surface area to total heat output. Additional heat loss from the boiler jackets eventually offsets any incremental gain in combustion efficiency. For this reason, it seldom makes sense to use more than eight boiler stages.

An inherent limitation of multiple boiler systems using on/off burners is that capacity must be controlled in steps, rather than as a continuously adjustable process. Although more stages reduce the height of the stepped heat input, the ultimate form of capacity control is a fully modulating boiler plant.


The Next Step

The newest concept in multiple boiler systems is multiple modulating boilers. Rather than using a simple “on/off” burner, modulating boilers vary their rate of fuel input and thus control their heat output over a wide range. The small modulating boilers currently available on the North American market can reduce their firing rate down to 20% to 30% of full output rating.

The ability of a modulating boiler to reduce its firing rate is often called its “turn-down ratio” (e.g. the boiler’s full heat output rate divided by its minimum stable heat output rate). For example, a boiler with a peak output of 150,000 Btuh and a minimum stable firing rate of 30,000 Btuh would have a turn-down ratio of 150,000/30,000, or 5:1.

When modulating boilers are combined into a multiple boiler system, the overall turndown ratio of that system is significantly better than that of an individual boiler. If four of the boilers cited in the above example were used in a system, the overall capacity control range would be from a peak of 600,000 Btuh all the way down to 30,000 Btuh. Hence the system’s turndown ratio would be 20:1.

At low heat production rates, the heat exchanger of a modulating boiler operates at relatively low combustion-side surface temperatures. When such a boiler is matched up with low temperature distribution systems such as for slab-type floor heating, it is common for the boiler to operate with sustained flue gas condensation. Modern modulating boilers have heat exchangers constructed of stainless steel or cast aluminum to withstand the effects of such condensation. When operating in such low temperature modes these boilers are also capable of efficiencies in the 95%-plus range.

Small modulating boilers are designed as sealed-combustion devices. Most are sidewall vented, using PVC, CPVC, or other polymer tubing. Combustion air is ducted directly from outside to the boiler.


To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

JohnNY

Wow

Thanks again, Robert!

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Robert O'Brien

I've

been through this before!

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"