This article is relevant to configuring Power Genius hot water and appliance controllers for controlling domestic hot water cylinders.
Minimum and Maximum Temperature
Power Genius allows you to configure and control the minimum and maximum temperature values which are used to manage the power delivered to a hot water cylinder.
Typical settings for hot water cylinders that can be heated using solar electricty are 45 deg. C for the minimum temperature and 70 deg. C for the maximum temperature.
When the setting for the minimum hot water temperature is reached Power Genius will turn the hot water heater on at full load until the minimum temperature is reached. This temperature is measured at about the half way level on the hot water cylinder so that at least half of the water will be maintained at this temperature.
When the maximum hot water temperature is reached Power Genius will turn the heater off.
The lower the minimum temperature and the higher the maximum temperature setting the more energy the hot water cylinder will store from solar energy when solar energy is available.
A higher minimum temperature setting will reduce the time it takes for the hot water cylinder to heat up and reduce the chance of running out of hot water.
The maximum hot water setting should never be such that after mixing with cold water the temperature of the water at the faucet is above 50 degrees C to avoid scolding. For the safety of children a maximum temperature at the faucet of 45 degrees C is recommended.
Regardless of the temperature settings Power Genius will heat all of the hot water in the cylinder to the sterilisation temperature of 60 degrees C once per week.
Holiday Temperature Settings
To minimise energy costs when going on holiday it is recommended to set the maximum hot water temperature to 58 deg C and the minimum temperature to 10 deg C. The lower temperature will insure that grid energy is not used to heat the hot water. The exception to this is when the hot water cylinder is sterilised. Solar energy will be used to maintain the temperature at 58 deg. C which will minimise the amount of grid power used to sterilise the tank.
Australia hot water anti-scald Codes & Regulations
Australia's National Plumbing Code AS3500 requires that hot water is stored at a temperature above 60C (140F) and that hot water delivery temperature (at the plumbing fixture) shall not be above 50°C (122°F). The higher storage considers the effort to reduce the risk of Legionella bacteria formation in the system.
Canadian Anti-Scald Codes & Regulations
New Zealand Anti-Scald & Hot Water Cylinder Storage Codes & Regulations
Hot water tempeature at the tap (bath sink, tub, shower) must be 55°C or less. New Zealand building code requires that the maximum hot water temperature at the tap shall be 45°C or less for childcare centres, schools, homes for the elderly and similar facilities.
Typical sources give the ideal hot water temperature setting for hot water cylinders in New Zealand as 60°C in order to keep water hot enough to kill bacteria inside the heater. Higher temperature settings in the cylinder are not necessary and increase water heating costs.
Watch out : 60°C is not the temperature of water that should be delivered at the tap or plumbing fixture - that temperature will cause scalding burns.
See NZS 4617:1989 Tempering (3-port mixing) valves, Date modified: 28/11/1989 regarding Tempering (3-port mixing) valves
Requirements for tempering valves for storage hot water systems particularly in domestic situations where hot water poses a hazard. These valves are intended to prevent scalding in locations such as homes, schools, motels and residential premises, where ideally all hot water outlets should be sourced from a tempering valve. Provides for valves suitable for water inlet temperatures of up to 100 degrees C.