Final Considerations
1. Understanding the energy effect of short-cycling is sometimes made easier by thinking of the issue in terms of the boiler’s operating cycle. During pre- and post-purge, the boiler is a reverse heat exchanger that takes heat from the system and throws it up the chimney. When the flame is established, the boiler first replaces this purged energy and then replaces the energy consumed by the heating system. The higher the percentage of time spent turning on and shutting down, the higher the percentage of total heat that goes up the chimney.
2. Light load devices are often found in fire pump systems, house pump systems, and chiller plants. Walk into a boiler room and what do you see? The boilers are all large, all the same size, and all too big for the micro loads. Why don’t we use jockey boilers? It seems that the boiler plant is the only building mechanical system that does not include a light load machine. It’s time to change that and make a light load boiler a standard part of every boiler plant.
3. Some engineers have reminded us that there will be radiation and convection losses from the buffer tank (if one is required by the system), and that this represents a permanent parasitic energy loss. That’s true; but the energy savings achieved to date have been so dramatic that we now dismiss this objection as unimportant. Remember that improving cycle efficiency produces savings of 15% to 50%, and often more. If the cost of
achieving this is a 0.25% loss at the tank, it’s a price that should be paid. Remember too all of the secondary advantages identified above. It is certainly possible to design a system that connects the buffer tank to the
system only when it’s needed, only during times when the system does not provide a “home for the heat,” but doing so adds cost and complexity, and the owner’s future fuel bills will depend upon the understanding and skill of the service technicians who will come and go in the years ahead. It is likely that many of them will not understand what the system does, why it must do it, how it does it, and how to optimize its performance. We
should pause and reflect before giving up the bullet-proof characteristic of the approach proposed here.
4. This approach is bullet-proof: it works no matter whose equipment gets purchased by the contractor.