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Early discussion is essential for heat pumps

One of the recurring problems in the renewable energy industry today is incorrect system design. Many horror stories circulate about heat pumps and their lack of performance; this is, almost without exception, the result of bad design.

The cause is usually a lack of understanding and poor communication between the consultant engineer and the heat pump specialist.

Heat pump specialists will be able to provide the client with a system and control options that best suit their application. In most cases the specialist is not involved until the contract has been let to a main contractor.

This is often too late to make changes to the system that are necessary to provide maximum possible efficiency and lowest possible running costs without incurring additional, unbudgeted expense.

Early discussions could, in the vast majority of cases, ‘design out’ such system problems. For example, designing a building’s heating and cooling emitters to operate effectively at lower flow temperatures for heating and higher flow temperatures for cooling.

Also, where an additional heat source such as a boiler is desired or required, for whatever reason, careful consideration needs to be given to the way this is integrated to avoid its over use.

Another issue is the production of hot water: although not operating at the levels of efficiency possible with space heating, the units are perfectly capable of producing large quantities at a usable temperature.

This makes best use of the considerable capital outlay involved in a heat pump installation.

As important as the internal design is the collector array. This involves many factors that need to be considered - peak demand, ground conditions, available space and duty of heat pump, all of which can have a dramatic effect on the success or failure of a project.

Sometimes these shortfalls and subsequent system faults do not become apparent for a number of years. So with this in mind, we feel that the design role of the specialist is crucial.

Surprisingly, many systems are still designed without weather compensation. This results in the heat pump having to be configured to provide a fixed flow temperature, often at a level beyond the most efficient operating range of the heat pump.

Most heat pumps have weather compensation as part of their normal operation and some have controllers that are also capable of many of the functions traditionally performed by a building management system.

The main issue seems to be an assumption that the heat pump delivers heat, should be hydraulically installed and should be controlled in the same way as a conventional boiler.

Ensuring correct design is crucial as each degree increase in heating flow temperature will result in an increased running cost of a heat pump of between 2-3 per cent.

One of the main drivers for installing this kind of equipment is the potential savings in terms of carbon footprint and running costs.

Without careful attention to some basic system ‘design rules’, there is a danger that systems will be installed that will not deliver the desired savings for the lifetime of the installation.

Neil Otter is operations director for Ecovision