Allenbourn Middle School, Wimborne
Sector: Education
Building: School refurbishment
Products: Purewell Variheat mk2 condensing cast iron boiler
Application: Space heating 285kW
Urgent replacement needed
Allenbourn Middle School’s old heating plant – three condensing boilers from ca. 1994 – was getting old and unreliable. As a school, funding is limited, but reliability is essential. In September 2018, one boiler broke with another one partly working and one running normally. Shortly after, the next one broke and a necessary replacement was identified, as spare parts for repairs were no longer available.
Having worked on several other capital projects with the Wimborne Academy Trust which looks after the school, Coomber Associates were appointed to undertake the design, tendering, health & safety and contract administration of the replacement boiler plant.
The solution
The school boiler replacement was completed over the winter months. To maintain school heating during this period, a temporary mobile boiler plant was required. A temporary plant room in the form of a trailer with two of Hamworthy’s Stratton mk2 S2-150 wall hung boilers was provided.
Stuart Giles, engineering technician at Giles Heating and director at The Temporary Boiler Company, commented on the reason the Stratton mk2 boilers were chosen for the trailer,
“When we built our temporary boiler plant on behalf of the Temporary Boiler Company, we wanted to make the most reliable, efficient and versatile system possible. Choosing two Stratton 150kW wall hung boilers was an obvious choice due to their high turndown ratio, stainless steel heat exchangers, spark ignition and C13 flue systems. Being a lightweight wall mounted boiler meant installing the boilers on an internal frame gave us space to fit pump equipment and a plate heat exchanger for hydraulic separation to protect the boilers. This is particularly necessary when they are used on older systems, as sludge from old pipework can damage the equipment. Instead, the old circuit stays separate from the new circuit. The BMS 0-10V interface built into the LMS boiler controls platform made easy work for the Building Management System (BMS) of the school, so we know via remote monitoring that the temporary boiler is working perfectly.”
The mobile plant room provided heat for three weeks during which the replacement took place. Other than the temporary plant, the difficulty of the project was to find boilers that would suit an old system and be compatible with the existing pipework.
Fortunately, the Hamworthy Purewell Variheat mk2 cast iron condensing boilers fitted the bill with a similar footprint as the old boilers to sit on the same plinths. The cast iron heat exchanger with 10-year warranty and large waterways deals well with existing debris in older heating systems. The three boilers deliver an output of up to 285kW (50°/30°C) and can match the heat demand with a turndown ratio of 9:1.
Stuart added,
“We use the Purewell Variheat boilers wherever possible due to their cast iron reliability. We avoid using aluminium boilers due to unreliability in case of bad system water quality and extra maintenance involved. Since changing over to the Purewell Variheat mk2s with the upgraded LMS controls platform and spark ignition system, we will continue to be using these for the foreseeable future. We like using Hamworthy because technical advice is always at the end of the phone and being a local family run firm, we like to use a local manufacturer.”
On changes for the installation of the new boilers, Stuart noted,
“We have reduced the boiler outputs from 120kW to 95kW per boiler as part of the design. Additionally, we have installed weather compensation, so the heating system only turns on when needed according to outside temperatures. The lower output boilers in combination with this and closer load matching thanks to the high turndown ratio means we’re effectively reducing energy wastage and are hence expecting a reasonable gas saving and higher efficiency of the system.”
Oliver Coomber, Director at Coomber Associates, who looked after the project commented,
“Being a company local to the site and previous excellent customer service we had no reservations about specifying a Hamworthy product to be installed. The appointed contractor, Giles Heating, used their own temporary boiler plant to complete the replacement to a high standard and within the timescales required. The newly installed boilers were handed back to the client within the programme period and under the original budget. We are very satisfied with the result.”
Paul Becher, Health, Safety and Facilities Manager for Allenbourn Middle, St John’s & Witchampton First Schools as part of the Wimborne Academy Trust, added,
“We are very happy with the work that has been done. All the contractors were polite, organised and worked in a tidy fashion with little disruption to the school workings. The boilers are working well and everyone I have spoken to is happy with the temperature within school. The plant room was left clean and tidy. I would happily recommend everyone involved for future work.”