This team of workhorses can save money for your school. A regular contributor explains how planning, selecting, and installing with attention to these details can pay off.
Modular boiler systems have been gaining in popularity since the energy crisis of the 1970s due to their compact design and energy efficiency. Combined with a microprocessor control unit, the system makes a perfect prime mover for your school or commercial or institutional building. Modular boiler systems are appropriate for either new construction or as retrofit solution to that high-maintenance energy hog in the basement.
Boilers installed in commercial and institutional buildings from the 1930s to the 1970s were likely to be fire-tube packaged steam boilers with power burners rated at 4,000 to 8,000 lbs/hr or less. These boilers were sufficiently large that in many cases the building was erected around the boiler, making removal of the boiler difficult.
The easiest solution was to replace the single large boiler with several small boilers. The small boilers were of a sufficiently compact size that they could be brought in through the front door, carried in elevators or even moved down stairways if necessary. The units could be placed in any arrangement, making the best use of the space and often accommodating new equipment to boot.
The process was time-consuming, but it didn't cause the closure of the building. Business went on as usual.
DO MODULAR BOILERS SAVE ENERGY?
There is no question that modular boiler installations save energy over existing old, inefficient boilers. But do they save energy over new models of the traditional fire-tube designs? The answer is a qualified -yes--the array saves energy by improving combustion efficiency and reducing jacket (skin) losses.
Although boiler heat transfer varies considerably for different designs, modular boilers generally provide higher combustion efficiency through closer control of the flame/coil interface. In addition, modular boilers reduce jacket losses because each one loses heat through the jacket only when it fires, and each one fires only as it is required.
Therefore, jacket losses are approximately proportional to load. For a large boiler, jacket losses are nearly constant regardless of load, and this reduces their low-load performance.
On the other hand, a single, larger boiler will have more heat transfer surface per BTU of load at low loads, as compared to the corresponding modular array. This helps its performance at low loads and somewhat offsets the increased skin losses.
To complicate matters further, either type of installation can he equipped with forced air ("power") burners, modulating fuel controls, combustion air dampers, and a variety of other accessories that will also save energy.
Still, all else being equal, the average modular boiler system saves energy over the average single or dual boiler installation, although this savings is probably only a few percent. This means that although modular boilers may be an easy choice for restricted space retrofits, other factors need to be considered for new building applications.
WHEN DOES A MODULAR SYSTEM MAKE SENSE?
First of all, is a boiler required at all? If it is possible to heat the building with gas-fired forced-air furnaces or gas-fired rooftop units, these alternatives might save first cost and operating cost. However, forced-air systems have definite limitations when it comes to building size, comfort, noise, and longevity. Most schools and other institutional buildings are built to provide consistent, quiet, and effective operation for many years. For this reason, hydronic (or steam) systems are frequently the best choice.
Steam heating systems are rarely used in new construction, but some buildings need steam. For example, medical facilities and laboratories need steam for autoclaves and other equipment. Any building requiring a 100% outside air system may need a steam coil to temper outside air. If a building has a large steam load, modular boilers are probably not the best choice. Although modular steam boilers can be piped together, this is unusual and exposes the owner to an increased danger of error in design and operation.
However, if a building has only a minor steam load, it may be possible to provide one or two modular steam boilers for the steam load and use several others for space heating. In this way spare parts can be minimized while reaping the energy savings of the modular system.
If a steam requirement for kitchen equipment is a roadblock, gas-fired equipment such as kettles and warming tables are usually available. It is generally not a good energy decision to install a steam boiler for a building when the only steam loads are kitchen equipment. A hydronic system will be easier to control, simpler to maintain, and will reduce energy bills as compared to a steam system.
SELECTING THE RIGHT BOILER FOR THE JOB
Small hydronic boilers suitable for modular installations come in a wide variety of shapes and sizes. They can be manufactured of different materials, fitted with a variety of burners, and configured to burn any fuel. Small boilers should be completely factory-assembled and -tested with no field assembly required. This labor savings is an important factor in the payback of the system and vital to the reliability of the boiler array.
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