Getting pumped up over carbon
John Durbin discusses how you can exploit the benefits of air-source heat pumps and why they will be crucial to achieving targets for reducing carbon emissions.
Energy efficiency has moved from the margins to the mainstream in recent years as the UK has become increasingly concerned with climate change from both a financial and environmental perspective.
This concern has been coupled with speculation and discussion about the technologies that will be best suited to create the energy-efficient, low-carbon buildings of the future. Rightly so; if we are to achieve the 60% reduction in CO2 by 2050 that has been made binding in the Climate Change Act, new and existing buildings will have to be made less carbon intensive.
This will require careful thought to decide which are the best materials and technologies that can be used to reduce CO2 while also being cost-effective. After all, building owners and occupiers will not invest in energy efficiency, and therefore CO2 reduction, if the payback period is prohibitive.
So where do we invest?
Heating and cooling are among the primary users of energy in both domestic and commercial premises, and significant improvements in efficiency can be achieved. Currently, heat pumps are the best technology to deliver energy efficiencies and reduce carbon from heating and cooling and are already widely being used in air-conditioning systems.
Most recently, a new report, ‘Building a low carbon economy’ from the Committee on Climate Change, which advises the Government on emission reduction policy, states that use of renewable technology, like heat pumps, will be central to achieving the UK’s emission targets —further strengthening the role of the technology. Moreover, late last year the European Parliament adopted the EU Directive on the promotion of the use of energy from renewable sources, which for the first time recognised heat pumps as a renewable energy technology. The directive text implies that member states should promote heat pumps as they have been with solar or wind energy.
Of the two primary types of heat-pump in use, air source and ground source, we at Daikin believe air source offers the best solution in both the short and long term. As a recent BSRIA report detailed, air-source heat pumps are similar in operation to ground-source heat pumps, except that heat is extracted from the external air rather than the ground. Air-source heat pumps are classified as either air-to-air or air-to-water, depending on whether the heat-distribution system in the building uses air or water.
The main advantage of air-source heat pumps over ground-source heat pumps is their lower installation cost. A ground-source heat pump requires a network of underground coils to extract heat from the ground. Air-source heat pumps extract heat directly from the outside air.. This makes air-source heat pumps suitable for new build and for retrofitting existing buildings — an important consideration in that much of the UK’s existing building stock will need to be made more efficient to reduce carbon outputs. The ground space and construction work required for ground-source heat pumps means they simply will not be an option for many existing premises, particularly those in urban areas.
Air-source heat pumps can have a number of environmental and operational advantages. For a start, more heat is supplied to the building than energy is consumed by the heat pump.
An air-source heat pump with a COP of three will supply 3 kWh of heat for the consumption of 1 kWh of electricity. If the heat pump is replacing (or being used as an alternative to) electric space heating, the use of the heat pump will offer significant carbon savings.
Heat pumps also open up the option of heat reclamation, which adds further efficiencies. Heat recovery is achieved by diverting exhaust heat from indoor units in cooling mode to areas requiring heating, essentially providing ‘free heating’. However, the primary advantage of heat-pump-based air-conditioning systems is to provide energy-efficient heating and cooling with maximum flexibility so the system can be designed according to the needs of the project — a consideration that is becoming increasingly important for reasons of productivity and operational costs, as well as the environment.
In recent years, design styles for intelligent buildings such as hotels, banks and offices etc. have increasingly featured large areas of glazing with attendant high solar heat gains that can only be dissipated by air conditioning. The increasing use of electronic office equipment raises thermal loadings further still to a point whereby, even in winter, internal temperatures can reach uncomfortable levels. The demand for cooling or heating can also vary considerably throughout the day depending on the number and occupation of personnel on the premises. But end users have come to expect far more than just cooling and heating from their air conditioning.
The ideal modern system must be energy efficient, easy to install, flexible, reliable and user friendly. Fresh air must be supplied without increasing energy consumption, and the role of central management facilities should also be considered for medium to large sized buildings. Modern air-source heat-pump air-conditioning systems meet all these demands.
Despite their proven performance, a criticism that has been levelled at air-source heat pumps is their COP in lower temperatures. During the heating season the outside air temperature is often low, but this does not negatively affect the performance of the air conditioning system. Daikin’s VRVIII series, for example, operates at outdoor ambient temperatures down to -5°C in cooling mode and down to -20°C in heating, more than meeting the needs of UK applications. Indeed, air-source heat-pump air-conditioning systems are installed and operating very effectively in Scandinavian countries, where temperatures fall much lower than most of Europe.
With the performance of air-source heat-pump air conditioning proven and given their suitability to new build and retrofit, the technology is sure to be important in measures taken to reduce CO2 emissions. The challenge going forward is making sure heat pumps are used to their fullest potential. Like most technology, heat pumps will only produce their greatest benefits if they are fully understood by specifiers, installers and users. And with this in mind, it is clear that we all have a role to play.
John Durbin is engineering department manager at Daikin UK.
