Task 2 – Systems and Concepts
In the analyses of the domestic hot water systems a greater comprehension of their actual performances is needed. The overall efficiency of domestic hot water is influenced by several aspects inside and outside of the dwellings. In order to make an objective comparison of domestic hot water heat pumps with other technologies performances are compared based upon:
- Performance of the water heater, where the real performance is not the same as in the test situation in the lab.
- Domestic hot water draw off patterns, often resulting in many small amounts of hot water in the kitchen and large amounts in the bathroom and dependent on the behaviour of the consumers. In most calculation models this difference is often not taken into account.
- Stand still losses of storage tank.
- Tapping efficiencies related to stratification (thermoclyne dinamics) in the storage tank.
- Temperature of stored hot water.
- Length of in-house piping from generator to tap, where often the distribution losses are much higher than in theoretical models. This is especially of great effect in Mult-Family Buildings.
For calculating the Energy Performance of Buildings a number of these factors are taken into account, based upon standards and test procedures, which are theoretical and often not supported by practical experience. Calculation models for the Energy Performance most often do not compare alternatives and take not into account innovative concepts. With the great number of potential alternatives and combination of renewable technologies this is a hindrance to further deployment of these technologies. Also on micro level designing system for domestic hot water in projects, calculation models are used, using the same basic ingredients.
At policy level more aspects are involved in the decision making for the right policy choices. A model then has to take into account the energy chain from source to end user. What is the energy mix for power generation and what amount of hot water will the end user get from the tap? This over the life cycle of the installation. Main aspects here are:
- Temperature level needed through legislation to prevent legionella growth in the system
- Transport and distribution losses through heat losses and distribution pump energy in collective systems for multifamily buildings and distric heating systems.
- The actual efficiency of electrical power generation and the development over the life cycle of the generator or the overall system.
- Type of fuel and heat generating efficiency in collective systems, ranging from gas or coal in a power station or local cogeneration to waste incineration and bio fuels.
An example of such a study was presented by Geelen at all at the 11th IEA Heat Pump Conference in Montréal 2014. This study was finaced by the Dutch Ministry of Economic Affairs.
An important focus of Task 2 is to use the real practical figures and therewith develop a model to be able to compare alternatives and innovative combination of technologies.