There were several very common attributes of the heating system at MWS that made it a great candidate for replacement.
- A single, oversized boiler kept hot 24×7 throughout the heating months.
- A large distribution circulator running 24×7 throughout the heating months.
- A control system that allowed setbacks to be accidentally overridden indefinitely.
The Oversized Boiler
If you put a Mack truck’s engine in your VW Jetta and drove by alternately flooring the accelerator and slamming on the brakes, do you think you’d get good mileage? Would the car last very long? Of course not. However, this is a direct analog to the heating system present in many, many facilities.
First of all, you can improve matters by putting the right engine into the car, as it were. Actually, it’s much easier to right-size a boiler plant by breaking it into multiple boilers, each capable of providing a portion of the heat needed. Think of it as the hybrid car with two motors: the electric motor and the supplemental gasoline engine. Two engines, one car.
In this case, we’re installing multiple lower-capacity staged boilers. This means that at low-load situations (cool Fall weather, for example), a single, variable-output pellet boiler can handle the base-load heating requirements. This constitutes the first stage. In fact, this variable-output boiler–the Fröling P4–can provide more than 90% of the heat needed by the school throughout the course of a heating season. In the very coldest weather, a “peaking” (i.e., satisfying the peak heating load) oil boiler kicks in and supplements the heating delivered by the base-load boiler. This constitutes the second stage. As a safety precaution, we are installing two identical peaking oil boilers so that if there are any issues with one boiler (oil or pellet), the other two can handle the heating while adjustments or repairs are made.
By installing several smaller boilers (including one that has variable output), we are able to avoid overpowering the system with too much heat. This arrangement minimizes wasteful on/off cycling of the equipment and allows each appliance to run at high efficiency.
By controlling the boilers more effectively, we’re able to avoid keeping them hot (= heat lost up the chimney) when heat is not needed by the building.
The Oversized Circulator
A single, 1-hp circulator ran 24×7 throughout the heating season. What would you expect happened when just a single zone valve opened? The water screamed through the pipes, creating noise and possible erosion. Never mind the wasted electricity…
We decided to install a variable-speed, ECM circulator (Grundfos Magna) to handle the distribution of heat throughout this zone-valved system. Even if it had to run at 100% output to duplicate the old circulator’s flow, it would use only 1/2 of the electricity. However, it meters its output to provide just enough flow to satisfy the current needs of the building, whether there are 20 or 2 zone valves open. Of course, it will be off when no heat is needed.
Heat on each floor of the building was governed by a timer that enabled that floor’s thermostats. If the timer was in an off cycle (such as at night, or on the weekend), people using the building could toggle an override switch that kept the thermostats active until the switch was turned off. Unfortunately, it was very common for this switch to be forgotten and left in the override position for days on end, needlessly wasting energy. In addition, the timers would need periodic resetting due to Daylight Saving Time/Standard Time and power outages. These corrections were not always performed in a timely (haha!) manner.
As part of our new control system, we will be incorporating a single timer that needs no adjustments. In addition, the override switches will be replaced with mechanical crank timers, so that accidental indefinite overrides are no longer possible.
These simple, yet powerful, design and control modifications will help the new heating plant use less fuel, less electricity and will require fewer repairs. As part of the Xylogen Thermal Service Agreement, both the school and we will benefit from these improvements. Stay posted to see how much we can save together!