Water Heating Systems
Solar Thermal Water Heating
Solar thermal water heating has the lowest running costs of all water heaters, meeting over 50% of a building’s hot water needs by using free solar energy. They are also environmentally friendly, as they minimise the need for gas or electricity. However, a backup or ‘booster’ system, such as wetbacks, may still be required for times when there is not enough sun to meet hot water demand. In some cases solar thermal heaters can be connected into your current system - check with your plumber.
Heat Pump Water Heating
Heat pump water heaters (or HPWH) work similar to a heat pump air conditioning unit. They draw heat from the outside air and use it to heat your water. Because it uses electricity to ‘move’ heat, rather than produce it directly, HPWHs are extremely efficient and cheap to run. However, they have a higher upfront unit and installation cost. Because they draw their heat from the air, you will need to select a model designed to operate in low temperatures if you live in an area with a cool climate.
Electric Hot Water Cylinders
Electric hot water cylinders are a common form of water heating in New Zealand. They have the lowest upfront cost of all water heating options, but are not very efficient and thus relatively expensive to run. This is because some of the heat in the stored water is constantly lost into the air and through radiation, a phenomenon called ‘standing loss’. One key advantage is that certain cylinders are available with additional connectors that allow other water heating options, such as solar thermal, to be added in the future. If you can’t afford to upgrade your cylinder that was manufactured before 2003, make sure to an install an insulation around it to reduce standing loss.
Continuous Flow Systems
Continuous flow systems can be powered by gas or electricity, and are designed to heat water instantly as it passes through the unit (without storing it). This means there are virtually no standing losses of heat, meaning they are efficient and well suited to buildings with variable usage patterns, like sports clubs. It’s important to note that gas is not a renewable resource, and produces greenhouse emissions when used. Electric models are available, but require separate heavy-duty wiring to accommodate the high currents required, and may struggle to provide enough hot water for larger sports facilities.
Gas Hot Water Cylinders
Gas hot water cylinders are similar to their electric counterparts in that they are relatively cheap to buy, but expensive to run due to standing losses. They can be located outside, useful where space is an issue.
General Design Tips
Look to reduce your hot water usage first. This allows you to specify a smaller system, reducing upfront and running costs. Installing low-flow, timed-use fixtures is a great way to achieve this.
Place the system as near as possible to where the bulk of hot water will be used. This minimises pipe length, in turn reducing the amount of heat lost through them.
Pipe lagging insulates your pipes, reducing heat losses. If plumbing work is being done, make sure lagging is fitted to any new hot water piping.
Check out the EECA water heating calculator. This tool lets you compare estimated upfront and running costs between different types of water heaters based on your usage.