Sizing up energy savings can be done in the water heating market

Developments in water heater sizing methods have allowed energy managers to maximise cost and energy savings. Chris Meir of Andrews Water Heaters gives his top tips for choosing the right product.

When selecting a hot water system for any commercial building, accurate sizing is extremely important. Finding out what the customer’s hot water needs are will ensure that any plant purchased will meet their expectations and demands.


Traditionally, water heaters were selected based on the demand of the building they would be installed in, with the flow rate calculated based on ‘demand units’, i.e. basins, showers, baths etc. There wasn’t as much diversity in system specification as there is now and many systems were oversized.


However, oversized systems are problematic, even if end users don’t realise it. The capital outlay is greater on larger plant, more energy is used in operation, and, if the demand for hot water is not there, it will cost the end user more in energy bills. This is all before we consider that larger plant takes up more space, and can therefore hamper installation.


Andrews Water Heaters saw the issue of oversizing in the industry and recognised the need for a handy tool which could accurately size products. The Size-it tool, first launched 20 years ago, is based on information from the CIBSE Public Health & Plumbing Engineering guide part G2, which states that a building’s total daily hot water usage is relevant to the assessment of the peak demand. It also recommends that a diversity factor of approximately 80 per cent should be considered, for more accurate sizing and to ensure the building is prepared should there be any uplift in peak demand.


Size-it is very simple to use tool – specifiers just input the customer’s hot water requirements and find the right products for the job, based on the property type. The sizing guide is based on a system design and a minimum temperature of 50oC, in line with the latest Building Regulations. A new and improved version of Size-it will be released this year and specifiers will be able to access it across all online devices and operating systems.


Direct gas-fired storage water heaters are a great solution for commercial premises and there are several different kinds on the market. Some have one burner, which gives them a high rate of recovery, and some have multiple burners to provide both high rates of recovery and built in redundancy. This means that each burner can work independently if the others fail, ensuring a more reliable hot water supply for end users.


With a correctly sized and correctly specified hot water system in place, it can closely meet the individual needs of the end user and runs at its maximum efficiency for energy and cost savings. But this is by no means the end of the story. To ensure a hot water system continues to run at its optimum performance, water treatment should be considered as part of a thorough maintenance programme.


The main culprit for hot water system breakdowns is lime scale. Lime scale develops more rapidly in hot water, so hot water cylinders, water heaters and calorifiers are particularly at risk. Research shows that deposits can begin forming as soon as a water heater is first installed and commissioned.


The most straightforward way of reducing lime scale is to choose water heaters with a stainless steel, low water content heat exchanger, as it is more difficult for deposits to form on the exchanger surface. Increasing the water flow rate can also delay the build-up of limescale. As it’s very difficult to remove once its formed, the most effective solutions are based around prevention. One recommendation is to fit an electrolytic scale inhibitor. This device is attached at the point of supply to the water heater and utilises the ion exchange process to replace high levels of calcium and magnesium salts in the water with sodium salts, softening the water.


Another option would be to fit a physical water conditioner/magnetic water conditioner. This device works by using a magnetic field to alter the physical characteristics of the minerals in the water supply, preventing limescale from forming.


It’s worth remembering that silt and sludge can also collect inside a water storage tank and can cause similar issues to limescale, in terms of impaired performance and added maintenance. Periodic flushing of the system as part of a regular maintenance schedule can easily remove it, or a sediment filter can be fitted at the point of entry to stop it at the incoming water supply point.      


The accurate specification and maintenance of hot water systems for commercial applications is essential to ensure any water heater can deliver a consistent supply of hot water on demand while keeping energy bills low. To ensure end users get maximum benefits, building managers must ensure water treatment is considered as a key part of the installation and ongoing maintenance recommendations so that poor water quality doesn’t let down users later down the line.

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