Understanding “Off-Peak” Heating in a Hot Water System

February 21, 2019

As a rule, “Off-Peak” heating employs a scheduled activation mode. To make the schedule work, the equipment includes a storage tank, which turns on its electric elements during off-peak hours. That’s a good enough description of a power-saving solution, but it skips a few facts. For one thing, what on earth is Off-Peak energy?

It’s Low-Demand Energy

If there is such a thing as low-demand energy, when is it available? To answer that question, think about how electricity consumption varies throughout the day. In the morning, the meters at a power station fly upwards as everyone wakes up to make breakfast. In the evening, the consumption figures drop, well, they do until a commercial break occurs during a favorite television show, then they peak again. Finally, into the night hours, everyone goes back to bed. Consumption figures drop. As a consequence, the cost of electricity also drops. This, in a nutshell, is Off-Peak energy.

Off-Peak Hot Water Systems

Common sense says we can spend less money on our electricity bills when we consume electricity at night. For during that period, electricity tariffs drop. All well and good so far, but how does a hot water system take advantage of this electricity plan? Well, strangely enough, the answer comes down firmly on the side of storage heaters. Although generally inefficient because of tank-related energy losses, tanks can store water. Better yet, they’re designed to store thermal energy. Now, all we need is a multi-function timer. As the low-cost tariff hours approach, the storage tank, which has been inactive all day long, automatically turns ON. Its elements warm, the stored water accumulates energy and the electric meter ticks around slowly.

A Next-Day Utilization Plan

Now that the thermal energy is stored, the tank performs as a kind of energy battery. It retains heat until required. As the sun puts in an appearance and everyone wakes up, the power flips back over to full-peak. That’s okay, though, for the off-peak hot water heating system is still stockpiling energy. If someone turns on a tap, hot water flows, but now the electric elements ignore the need to replace the lost energy; they’re waiting for the night hours to spin back around again.

Low-power periods are used by power stations as a load management tool. At night, there are fewer people awake, so they can afford to drop the tariffs. Elsewhere, hydroelectric dams have turned their generators into pumps. They’re pumping the water back up top. Generally speaking, the energy focus shifts. Off-peak water heating units simply take advantage of that fact, and all it takes to expedite the scheduled mode is a multi-function timer and a fully insulated water storage tank.

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