M&V Solar Water Heating Guideline - Eskom

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Measurement and Verification Standard Guideline for Low Pressure Solar Water Heating Systems v1r1 2 Establish how , when and how much and for what purpose water is heating by electricity. 3 Establish the power in [kW] of the water heating device and evaluate the energy/demand used. The electrical water heating used at a low-cost household is based on average figures and often on the assumption that the water is heated by standard/conventional electric kettle with an typical installed power of 2 kW and a typical volume of 1.8 litres. The cold water temperature may wary by the season and is taken as Tcold = 16 o C . The water is heated until boil i.e. Thot = 96 o C (it assumed that the kettle switches off automatically at that temperature). The heating process efficiency ( ) is taken as 90% which takes into account losses if the water is heated not by kettle but by hot plate for example. The thermal energy for each boil ( Ehw) is calculated by: ) The corresponding electrical energy needed to produce this thermal energy is : 4 Obtain information for electricity and water bills for the household for crosschecking the information above. 30 the actual number of people living at the house might vary. Urban households would use more electricity than the rural ones. 1.This might be misleading since the households use predominantly prepaid electricity and when the balance is negative the inhabitants might use alternative means for heating water. 2. It might be useful to assume that all the water heated electrically in a household is done by an ”equivalent electric kettle “(2 kW) as it is in the majority of urban households. This would simplify the process of base line development. Note that, the water heated by the kettle for bathing, washing and cooking is always mixed with cold water in order to meet the volume and temperature needed. This might be grossly misleading since in most of the cases inhabitants do not provide accurate answers due to one reason or another. Note: An example for a typical house base line determination using interviews is given in section 10 below. 6.4.3 Using Base Line Measurements by Dedicated SWH data Loggers after the Retrofit The dedicated data loggers supplied by EA are shown in Figure 18 and 19.
Measurement and Verification Standard Guideline for Low Pressure Solar Water Heating Systems v1r1 Figure 19: SWH Data Logger The measurements obtained by the data loggers installed after the retrofit do not provide correct information about base line hot water usage. The amount of hot water used after and before the retrofit is not the same. However, they could be used to determine the performance assessment evaluation. 6.4.4 Measurements of the Electrical Energy prior and after Retrofit at the Household The most appropriate way is to measure the savings and determine the base line is to measure the electrical energy and determine the base line in combination with the interview as described in Section 5.3.2. above. Simple and inexpensive data loggers and CTs as shown in Figure 20 and Figure 21 could be used to measure the current at the household and thus to determine the savings in a way that the grid can “see” them. This will allow a precise measurements of time of use for electrical water heating appliances. Figure 20: A Current Transformer (CT) and its connection to a Data Logger is installed at a DB in a Low-cost House to determine the base line and energy savings by the retrofit. 31
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M&V Solar Water Heating Guideline - Eskom

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