Sector: Education and childcare
Building: Nursery refurbishment
Products: Stratton mk2 wall hung boiler, Halstock calorifier
Application: Space heating, 43kW, indirect fired DHW


Canterbury-based Riverside Children’s Centre is one of Busy Bee’s 342 nurseries in the UK. It provides childcare and cooked midday meals for children aged 6 weeks to 5 years, Philip Kiss, Building Services Engineer at Canterbury City Council, turned to Hamworthy Heating for a reliable and efficient nursery heating and hot water solution to replace the old boiler. The chosen system of stainless steel wall hung boiler and calorifier have already achieved cost savings of 16.7% after 7 months of operation.

The solution

The Stratton mk2 stainless steel wall hung boiler now delivers heating and hot water to the nursery.
The old boiler installed in the building was a Hamworthy Ferndown combination boiler (heat and hot water), rated at 70kW. To achieve further energy and cost savings, Philip Kiss, who has been working on a wide range of projects with Hamworthy, was looking for a suitable boiler replacement. A large enough hot water supply for meal preparation in the kitchen and other points of use throughout the building was crucial.

Ian McGregor, Area Sales Manager at Hamworthy Heating, has worked with Philip for many years. Focused on achieving maximum energy savings, he identified Hamworthy’s Stratton mk2 wall hung condensing boiler with stainless steel heat exchanger as an ideal replacement. The selected model delivers an output of 43kW, a gross seasonal efficiency of 95.75% and features an extensive Siemens LMS controls platform to deliver heat and hot water the most efficient way.

Philip comments,
“I have worked with Ian over many years and he had a clear understanding as to what we needed: Primarily reliable delivery with maximum possible energy savings. So, I was confident enough to let him take the lead on designing the boiler control regime.”
With a turndown ratio of up to 5:1, the boiler can match the heat load flexibly and efficiently from 8kW up to 43kW. The stainless steel heat exchanger with 5-year warranty has the added benefit of corrosion resistance which is an advantage for buildings or areas where the water is soft or has been artificially softened.

Additionally, flexible room sealed flue options and the ability to frame mount the boiler helped to achieve space savings. There is also room for the possible later installation of a second wall hung boiler, should the nursery be extended.  

To cover the hot water demand, the centre also required an adequate but not oversized water heater. The choice fell on a Hamworthy Halstock HS305UV stainless steel calorifier with a continuous output of 390 litres per hour at a differential temperature (the difference between hot water system flow and supply temperature) of 44°C.

This calorifier model is suited for combination with smaller output boilers such as the chosen Hamworthy Stratton mk2 wall hung boiler. 

The Stratton mk2's built-in controls are set to hot water priority mode.

Full heating temperature control

Ian explains the chosen boiler control strategy for the children’s centre
"We wanted to make full use of the built-in boiler LMS controls for controlling the heating and hot water. The Halstock calorifier heats up quickly – in only 38 minutes from cold. Adopting a hot water priority strategy, we can then switch off the heating circuit from the boiler and direct the full power to hot water production at maximum temperature in non-condensing mode – without anyone noticing. Heat up times are short, as the water in the calorifier is rarely cold."
Riverside Children’s Centre has underfloor heating on a single heating circuit which requires a maximum flow temperature of only 50°C. A higher temperature can lead to structural damage to the floors. With a return temperature of around 30°C, the boiler is condensing and working at its most efficient state.

Ian continues 

“If we only had a heating circuit operating at 50°C, it would be an easy control set up. However, because we also need to operate the boiler at 80°C for hot water production, the heating circuit (underfloor heating) must be protected from high temperatures. Without the LMS platform and its built-in hot water priority mode, the heating system design would be more complex utilising a variable temperature mixing valve. The boiler would also be constantly running at 80°C in a less efficient non-condensing mode. With a maximum of about 10% of the boiler operation requirement being for hot water, this would be a lot of wasted energy. The kitchen has the potential to demand high volumes, but in general, there is very little hot water demand in this building. We are mainly merely topping up the stored water taking only a few minutes at a time. 

The hot water priority setting on the LMS controls means the boiler knows exactly when hot water is required, shuts down the heating circuit to protect it and starts hot water production. 

After excess heat has been distributed around the hot water supply primary circuit, heating operation goes back to ‘normal’. This means we protect the underfloor heating circuit and save energy thanks to the controls setup. All this is done from the boiler itself, without the need for extra controls.
The Stratton mk2 stainless steel boiler was provided free of charge by Hamworthy as a test site for the new wall hung boiler range when it was launched in 2016.
The Halstock stainless steel calorifier was chosen due to its corrosion-resistance and quick heat up time.

Issues with hard water

Canterbury has very hard (temporary hard) water, caused by dissolved calcium hydrogen carbonate. Most of the water is drawn from artesian wells from chalk layers, therefore calcium scale is a serious problem. Rain water absorbs carbon dioxide from the atmosphere as it falls through the air, making it carbonic acid. Due to the acidic state of the water, the calcium is dissolved as the water passes through the ground. The carbon dioxide contained within the water is unstable and is released easily when heated or agitated, such as in the hot water system, leaving the calcium deposits behind. By boiling the water, the hardness can be removed which is why it is called ‘temporary’ hard water.  

To protect the heating and hot water system, the nursery had a water softener installed. This helps to eliminate problems stemming from calcium scale deposits which can cause serious damage to boiler parts and reduce the overall efficiency of a heating system. However, there is a downside to water softening.

Ian elaborates
“In soft water areas, or when the water has been softened, the carbonic acid is not saturated by dissolved hardness, therefore the acidic effect is more aggressive. This is why in soft water applications, stainless steel cylinders and boilers are preferred due to their corrosion resistance.”

Overcoming continuous heating supply challenges

The nursery was in constant use during the boiler and water heater replacement and could not be deprived of heating or hot water for significant periods. In the first phase, the Halstock hot water cylinder was installed over a weekend and initially run on an immersion heater connected to a local plug top. The original boiler, which previously delivered the heating and hot water, was then only providing space heating. To avoid any disruptions, the new Stratton mk2 boiler was installed out of the heating season. 

Philip concludes
“The biggest challenge was the planning, rather than technical issues. Two small WCs still have electric water heaters supplying them with hot water, but it is our intention to extend the pipework, so these are also supplied by the boiler.”
Gas savings were up after less than a year.

Gas savings after less than a year

When the new gas bill arrived in July 2017, the new boiler had been running for 7 months. 

Philip comments 
“For the year ending July 2016, our annual consumption was 152,433kWh at a cost of £9,545. For the year ending July 2017, it was 129,995kWh at a cost of £7,951 which means we’re looking at savings of 22,438kWh and £1,593. The new boiler has only been running for just over half a year and we’ve already saved 16.7% on expenditure for gas. It’s great to already be benefiting from cost savings. We’re looking forward to comparing bills again in 2018 once the boiler has been running for a whole year.”

Dependable energy-efficient heating supply supported by intelligent boiler controls

After the nursery heating and hot water upgrade, Riverside Children’s Centre now benefits from a reliable, highly energy-efficient stainless steel boiler coupled with a stainless steel calorifier with fast recovery time which effectively saves money. The automated controls ensure heat is supplied on a hot water priority basis, optimising energy savings in the form of only temporary non-condensing mode operation of the boiler for hot water production.

About working with Hamworthy, Philip adds

“I have enjoyed working with Hamworthy on this project because both their sales managers, Ian and Stuart, know what they are talking about and look after me. I know that I will receive sensible and practical answers to my questions.”

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