Quick fix or quick botch?

Published:  03 October, 2013

Sabien Technologies, boiler, dry cycling, space heating
Retrofit controls that complement existing controls — Tony Willis.

Quick fix’ energy-saving initiatives have the benefit of delivering a fast payback — but choosing the right ‘fixes’ and validating the savings are essential. Tony Willis explains.

As building operators look for ways to reduce their energy consumption and carbon emissions, so-called ‘quick fixes’ hold much appeal. The best quick fixes are relatively inexpensive to implement and will deliver benefits to the bottom line and the carbon footprint in a short space of time.

One key challenge for the building-services engineer, therefore, is to help end clients identify the most appropriate and fruitful quick fixes. Another is to ensure that the energy savings are measured and analysed accurately, in line with best practice.

Many quick fixes involve introducing additional technologies to existing systems, often to improve overall control of the system and align its operation more closely to the demands of the building and its occupants. In such cases it is clearly important to ensure that the selected technology will meet the client’s expectations with regard to savings without impacting on other important parameters, such as comfort.

This principle can be illustrated by considering measures to control boiler dry cycling, a phenomenon with which most mechanical engineers will be familiar. However, to quickly recap, boiler dry cycling occurs with most commercial and industrial boilers and describes the firing of the boiler in response to standing heat losses from the boiler itself, rather than a demand for heat from the boiler.

There are a number of products on the market that claim to control boiler dry cycling, and building-services engineers are ideally placed to sort the wheat from the chaff through their understanding of heating systems. So the manufacturer’s explanation of how their system works should make sense from an engineering perspective.

For example, it is obvious that boiler plant should be controlled on the basis of temperature, and the priority of the control strategy must be to maintain space temperatures at their set points and ensure availability of domestic hot water. So if a boiler control technology works by artificially lowering the boilers’ temperature set points, it may compromise comfort conditions in the building.

Similarly, if the technology under consideration controls boiler firing on the basis of time — such as by delaying the firing of the boilers — once again there is a strong chance it will impact on temperatures and comfort conditions.

A far more sensible and effective approach is to analyse the flow and return temperatures for each individual boiler every 10 s to provide a true load profile for each boiler. This enables the system to differentiate between a genuine call for heat and one that is simply firing to replace heat caused by standing losses.

Just as importantly, the system should recalculate the values every time the boiler reaches its required set-point temperature, so it adapts to building management system/optimiser variable set-points and does nothing to conflict with other existing controls.

Sabien Technologies, boiler, dry cycling, space heating
Boilers that fire just to offset their own standing losses are using energy unnecessarily, which can be eliminated with retrofit control technology.

This is an important point because it is a fundamental requirement that any retrofitted controls should work in harmony with existing controls such as the building-management system, weather compensation or boiler sequencing. Any retrofit control technology that potentially interferes with the operation of existing controls should be avoided.

Validating savings

A key part of scoping the project is to determine how energy savings are to be measured to ensure that any such measures are valid. For instance, if the provider of a boiler-control technology proposes measurement of savings based on boiler run times, this will not take account of the firing level of a two-stage or modulating burner. Therefore, boiler run times are not a true indication of energy consumption.

Consequently a clearly defined measurement and verification programme should be put into place. In the case of heating systems, energy consumption will be influenced by weather variations so it is vital to adjust the energy-consumption measurements using degree day data supplied by the Met Office.

When dealing with a number of variables it is reassuring to work with a Certified Measurement & Verification Professional (CMVP) who has certified under the International Performance Measurement & Verification Protocol (IPMVP). This ensures that person or company is working within in internationally recognised framework.

The changes in energy consumption over longer periods of time (pre, during and post project) can be established by CUSUM (cumulative sum) analysis, a Carbon Trust-approved tool that examines trends for sequential events, such as energy consumption, over time.

In an ideal situation it will also be possible to ensure that energy-reduction initiatives are carried out one at a time and that there are no changes in building usage that might influence energy consumption.

The general principles described here have been tried and tested in the installation of over 6000 of our M2G intelligent boiler-load optimisers. However, they are equally applicable to many different types of ‘quick fixes’ and other energy saving initiatives.

Tony Willis is technical sales director with Sabien Technologies



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