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Optimising space heating efficiency

Author : Tony Willis, Sabien Technology

06 April 2017

The efficiency and reliability of a space heating system are influenced strongly by the effectiveness of the water treatment regime, which may include innovative additives to improve heat transfer.

Given the contribution that space heating systems make to a building’s energy consumption and carbon emissions, it makes sense to ensure that such systems operate efficiently.

Very often, the main focus is on the heating plant – which is clearly important - but the distribution system is also worthy of attention as it influences both efficiency and reliability.

For example, the performance of a wet heating system is dependent on three key mechanisms of heat transfer to the heat emitters such as radiators – conduction, convection and radiation.

Conduction is responsible for the transfer of heat from the water in the system through the metal of the radiator walls to the outer surface of the radiator.

As the outer surface warms up it transfers heat to nearby air molecules in the space, causing them to rise by convection.

This movement draws cooler air molecules at floor level towards the radiator so that they too are heated, resulting in convection currents that drive the warmed air into the required heated space.

There is also some radiated transfer of heat through electromagnetic radiation due to the temperature of the radiator surface.

Consequently, the ‘health’ of the distribution system and its ability to transfer heat efficiently to heat emitters is critical to the overall performance of the heating system.

To that end, an effective water treatment regime is essential and there are two aspects to this.

The first of these is a water treatment strategy that protects the system and underpins its reliability – as well as improving efficiency.

This is particularly important in larger buildings such as offices, factories, hotels and hospitals where the reliability of the space heating is critical to the continued operation of the facility.

The second is a relatively new water treatment additive that further improves the efficiency of heat transfer from the water in the system to the heat emitters, resulting in added energy savings.

Protective water treatment

From the moment a system is installed it is at risk from corrosion due to the reactions between the water and the metal components of the system.

This corrosive process results in a build-up of sludge or magnetite - a black mud-like substance which is an accumulation of fine ferrous particles caused by corrosion.

Left unchecked this can cause a range of problems, including blocked heat exchangers and pipework.

It may also cause cold spots in radiators, damage to pumps and valves and, in some cases, premature boiler failure. Over time, the system will also suffer from reduced efficiency, higher energy costs and CO2 emissions and, potentially, higher capital investment on replacement parts such as boilers.

These risks are mitigated through the application of anti-corrosion and anti-scale water treatment programmes, which are well established and familiar to most building operators.

As such, they support business continuity whilst reducing energy bills, maintenance costs and environmental impact.

However, there are also other factors that lead to heating system inefficiencies due to reduced heat transfer from the water in the system to the surface of the heat emitters. Addressing these factors requires a novel approach, taking advantage of innovative water treatment formulations.

Improving heat transfer

Even in the cleanest, scale-free wet heating system there will be microscopic crevices and imperfections on the internal heat exchange surfaces of radiators and other heat emitters.

These effectively create gaps between the heating fluid and the heat exchange surface – gaps that the heating fluid is normally unable to enter because of its natural water surface tension.

This means that the heated water is not always in perfect contact with the inner surfaces of the heat emitters, because of the natural water surface tension and the system frictional resistance.

Now, a heating system additive called EndoTherm (recipient of CIBSE’s 2016 Energy Efficiency Award) reduces the surface tension within the fluid, enabling it to make closer contact with the heat exchange surface so that the conduction of heat from the water to the heat emitter is enhanced.

EndoTherm, is an organic based system additive that is fully compatible with existing heating inhibitors and heating system water treatment. Typical dosage to the system would be 1% of the total system volume, and will not require further dosing for 5 years under normal system conditions.

Independent ‘in field’ verification on over 50 projects has demonstrated energy savings of between 10% and 15 % and paybacks typically within two years. These projects involved many different building types, ranging from schools and leisure centres to offices and care homes.

Sabien Technology is the exclusive UK distributor of Endotherm for multi-site commercial applications.

Boiler load optimisation

As noted earlier, when optimising the efficiency of a heating system it is clearly important to consider the performance of the heating plant as well as the heat distribution system.

Yet, for a number of reasons, it is rare for commercial heating systems to operate at their maximum efficiency.

One of these reasons is that it is common industry practice to size boilers for the worst-case scenario of very cold winters – which are only occasional in the UK and generally limited to short periods.

Consequently, boilers often operate under part-load conditions for extended periods. This, in turn, may lead to boiler dry cycling and short cycling, both of which are wasting energy. Moreover, when the overall efficiency of a heating system is improved by installing Endotherm, this leads to temperature set-points being achieved more quickly, so that the boilers may be further under-utilised.

These issues of boiler dry cycling and short cycling can be prevented by installing Sabien’s M2G boiler load optimisation control, which has been shown to reduce the energy consumption of commercial and industrial boilers by between 10% and 25%.

Thus, Endotherm and M2G make an ideal combination when it comes to optimising the performance of a heating system.

Furthermore, qualifying organisations can sign up for a free pilot programme to evaluate these technologies with no financial commitment.

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