A smarter way of using heat pumps

Issue 41 – August 2012

This article by David Victor Tackie and Helena Segerberg first appeared in the International Electrotechnical Commission's (IEC's) e-tech, July 2012. It is summarised here with permission from IEC.

David Victor Tackie is one of the three IEC 2011 Young Professional Leaders. In collaboration with Helena Segerberg, a Consultant Engineer from Balslev who is working on a large Danish Smart Grid project, he talks of how heat pumps could be integrated into the intelligent system of the future. They would help deal with various coefficients of performance and in evening out power loads.

Reducing CO2 emissions

One way to reduce climate change is by lowering CO2 emissions. Much of the CO2 we emit into the atmosphere comes from burning fossil fuels – gas, oil, and coal – to generate electricity. In the developed world, some 40% of CO2 emissions are caused by energy consumed either for travel or in the home. So, how can we help reduce CO2 emissions?

Generating energy with heat pumps

When it comes to energy use in the home, a heat pump is one of the most efficient means of heating or cooling a building. Working based on heat transfer, heat pumps only require a minimum amount of electricity to function. So, they can transfer heat from a source outside the home, such as the air or soil, and pump it to another area inside the building where it is heated or cooled over a circulating coil system and then transferred on to provide hot water or air conditioning. For heat pumps, the average coefficient of performance (COP) – or power factor is approximately three: energy output is three times the amount input.

Need for international Standards

Since heat pump control needs to meet several objectives, such as optimising COP, information needs to be exchanged continuously between each heat pump and the Smart Grid. This means that the necessary intelligence is available about when and where power is needed and what power is available from what sources, including renewable energies. This allows the Smart Grid to make informed decisions and manage its power needs appropriately. It follows that there is a great need for International Standards.

Individual customers with heat pumps also need to be able to switch freely and easily between electricity suppliers. The emphasis is placed on an open platform, an authorised communication server, and a secure gateway into the house.

One of the most popular Standards series for this is IEC 61850 Communication networks and systems for power utility automation. These Standards are essential for Smart Grid management and the integration of Intelligent Electronic Devices into a Substation Automation System. Standards deal with all the elements of a power substation: its functionality, terminology, parameters, life-cycle management, and the relevant communication structures.

Where data security is concerned, an IEC Technical Specification, IEC/TS 62351-8 Ed. 1.0:2011 Power systems management and associated information exchange – Data and communications security – Part 8: Role-based access control is applied. IEC/TS 62351-8 concentrates on the security aspects of computer-based applications where access can be both human, via local wired or wireless media access, and remote, via automated computer agents or control centres.

Danish Smart Grid research project

Denmark is one of the world's leading suppliers of wind power and now it has initiated a vast research and development project called iPower. A 'strategic platform for innovation and research in intelligent power', iPower's mission is to develop an intelligent and flexible energy system that can handle fluctuating power generation, particularly where renewable energy is concerned. By developing the present Danish electrical grid into a Smart Grid, a large number of distributed energy resources, methods of storage, and energy-efficient devices can be incorporated. They include intelligent, regulated heat pumps, electric vehicles that can act as energy storage units when not in use, and photovoltaic modules for the production of renewable energy.

Smart Grid solutions include heat pumps

One working group in iPower is studying how Smart Grid solutions can be used to secure sufficient grid capacity in the low voltage grid. [Low voltage is defined by the IEC as voltages up to 1 000 V AC or 1 500 V DC]. It has also been analysing the effect of incorporating smart heat pumps using new control and communication technology.

Its analysis has shown that an increase in the number of installed heat pumps in the electric grid would cause grid capacity problems in many low voltage grids, primarily because the grid in many areas isn't designed for this scale of increase in consumption.

Even out the load

Current domestic heat pumps operate according to the actual heating demand. In other words, the warm water in a domestic storage tank is reheated immediately after consumption and then the temperature in the tank is maintained throughout the day. As most people in a district have similar habits, the variation between the maximum and the minimum load for the whole district increases along the same lines.

Smart heat pump control would enable the operation of heat pumps in a district to be coordinated so that the total load curve for all houses would be smoothed out. The following measures would help increase the flexibility of operation time for heat pumps:

  • increasing building insulation and size of storage tank used for warm domestic water

  • heating up domestic warm water just in time for use or at an optimum moment according to the total load on the distribution network

  • lowering the temperature at night time and when nobody is at home

  • increasing the insulation of the building and the size of the storage tank will mean that the heat pump has to operate less frequently. The storage tank can, for instance, be placed on the roof or buried outside.

A simulation was carried out on 24 December 2011 for a typical Danish low voltage network dating from 1970, supplying houses with an energy consumption that corresponded to this period. The simulations showed that, by coordinating the operation time for the heat pumps, further heat pumps can be installed in a specific district without the need to reinforce the low voltage grid. This can be achieved without any change in comfort levels, that is, the temperature in the house is maintained at 21ºC.

In the first simulation exercise, the heat pumps operated independently of one another. In this instance, heat pumps could be installed in 21% of all houses in the district. The size of the storage tank for warm water was 1 m3.

In the next exercise, the operational periods of the heat pumps were coordinated through direct control and the storage tank for warm water measured 2 m3. Here, heat pumps could be installed in 50% of the houses, resulting in the load curve being almost smoothed out. The main disadvantage for this network was the drop in voltage level for the houses at the end of the line.

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