Efficiency and energy saving with SCR relays in electrical heating

Let’s keep on talking about energy, renewables and energy saving. We’ve already talked on how is it possible to achieve energy saving in refrigerating groups using inverters, and how to increase efficiency in cooling tasks using dry coolers and evaporative towers.

While the use of inverters is quite affirmed on the cooling market, the use of SCR solid state relays with switching control is still not very much widespread on heating tasks. This is in fact a kind of application that we implement on Tempco’s thermoregulating units. When there is the need to heat a fluid, there are two options: a traditional boiler producing vapor, or diathermic oil or pressurized water, thus heated. The second option is to use electrical heaters. The primary energy sources employed are thus fossil fuels, or natural gas in burners, or electricity in the case of heaters.

Modulating burners are already very common in the market, enabling an adjustment of fuel consumption based on the thermal duty required. In case of electrical heating, the goal is to adjust the power capacity of the heaters. This is possibile thanks to SCR (silicone controller rectified) solid state relays. In this case, using a thermoregulating unit with a PID controller (proportional integral derivative controller), we can ask the heaters to provide only the effective power capacity required for the thermal duty needed at a certain step of the production process, in order to reach the temperature set-point or to maintain the temperature level.

The energy saving that can be achieved is really interesting. That’s because when engineering these kind of machines, they are designed to be able to provide the maximum heating capacity required. For example: an application requires to heat a certain amount of product inside a pharmaceutical reactor. The thermal duty is calculated by considering the starting temperature of the product and the final temperature to be reached, and the time lapse to achieve the heating task. With some additional power to the final result in order to also heat the reactor itself, and considering for example possible thermal losses. But once the final working temperature has been reached, the power capacity required becomes very much lower, only aimed to maintain that temperature level. For sure there will be the need to supply some more energy, for example in case of chemical reactions of the product, to compensate thermal dissipation or the heat loss through the coibentation. But, overall, this amount of energy will probably only be 1/10 of the design capacity, or maybe 1/3 or 1/5.

In order to adjust this power capacity, the solution employed in the past was to build multistage machines, equipped with different heating stages obtaining power adjustment using contactors or ON/OFF solid state relays, with the PID regulator switching these devices on and off in function of the heating capacity required.

The thyristor, or SCR solid state relay, allows to adjust the power capacity providing only the effective thermal duty required to maintain the temperature level within the proportional range, thus maintaining the set-point. Two main results are obtained, the first one being a relevant energy saving. While the second one, very important as well, is a much more accurate and fine regulation of the temperature.

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