Which Control System for Different Heating Systems?

Posted on 31st October, 2012

I was asked this question recently and although it is a wide-ranging subject, here are my thoughts:

 

heating programmer

Real-life experience shows generally that heating systems which use precise amounts of fuel (e.g. in a measured or controlled flow rate) such as oil, gas, electricity or wood pellets will benefit from a refined control system to a greater extent than systems which are subject to random or unmeasured fuel input - such as logs, peat, coal, anthracite, etc.

In other words, human-controlled fuel input will not have the same accuracy as an automatic system and it is therefore much more difficult to accurately predict the performance of the human-controlled systems.

 

There are anomalies of course. One system which can be a useful way of heating (and cooking) in smaller, square-plan houses is the masonry stove. These are called Russian stoves, Swedish stoves, Finnish stoves, etc.; depending on where they originate; however the principle is the same, namely that a looped flue delivers heat throughout a large mass of masonry during a single intense firing period in the solid fuel firebox. The masonry then heats the surrounding areas for as long as it retains heat. An oven is often incorporated above the firebox to take advantage of the available heat. This system is therefore not precise but can be very effective. A modern-day equivalent is where a log boiler heats up a very large water tank over a couple of hours and the water then delivers heat around the space heating system (usually underfloor pipes) over the next 18-24 hours.

 

The answer then, is that the control system must be matched to the heating system in a way that extracts the best possible benefits over a given period of time. Basic essentials for a hot water-based space heating system (which is the most traditional form in this part of the world) would therefore include TRVs (thermostatic radiator valves), room thermostats, boiler thermostats, a means of preventing the system from cycling cooler water through the system and of course a programmable timer which can set different heating levels for different zones in the house at different times.

 

Nowadays, I would advise most householders to consider a multi-solution system - for example; install an automatic gas, oil or electrical heating system to run along with a wood-burning stove (which incorporates a boiler) and solar hot water panels. A mechanical home ventilation system with an air-air heat exchanger could also be added (this is easier to do in a new-build, since properly installed ducting is required). Using a fully functional programmer, this type of combined solution allows you to make best use of the most economical heat sources at different times of the day or year.

 

As is always the case, you must compare capital costs with payback times. If you are going to be specifying or designing systems, you would be advised to create a spreadsheet for ease of comparing costs.

 

I hope this helps,

Les.

 

(Image from http://www.worcester-bosch.co.uk)

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