The prestigious St Paul’s Cathe dral has been standing at the highest point of London on Ludgate Hill since its latest rebuild over 300 years ago. As a Grade 1 listed building, the delicate building structure is subject to strict regulations, prohibiting alterations without special permissions. The cathedral faced failing boilers, which meant a heating and hot water plant refurbishment project would have to take those restrictions into account. The challenge was met by Hamworthy, British commercial heating and hot water specialist, who provided a modular boiler system and two high performance calorifiers.
The well-known cathedral’s existing heating system consisted of three steel shell boilers fitted in the 1960s which received a burner upgrade in the 1980s. Problems on the equipment occurred and were fixed until the boilers finally started leaking and could not be repaired anymore. At this point, Robin Bunton from Bunton M & E Services advised replacement boilers were necessary. Together with Mike Crouch, Hamworthy’s agent for the area, and Nick Coates from Blue Print Building Services Design, he worked on the specification for the cathedral’s heating and hot water refurbishment project with Clerk of Works Martin Fletcher.
Space-saving, energy efficient and powerful solution wanted
The cathedral was seeking reliable and energy efficient boilers to meet its high heating and hot water demand while keeping the running costs down. To avoid changing the flues, the cathedral initially planned to replace the older system with pressure jet steel shell boilers. Robin, however, recommended Hamworthy’s Wessex ModuMax mk3 condensing modular boilers to meet the reliability and energy efficiency requirements, as well as compliance with current legislation to eliminate inefficient boilers.
“We have used the Wessex boilers since they were introduced and we know they are a very reliable product. They are space saving, great in refurbishment projects and buildings where you can’t change the building fabric, such as St Paul’s. Hamworthy also has an excellent after sales and spares service, with their own engineers, which is why I prefer working with them.”
Old pipe system installation preparation
Six months prior to the installation of the boilers, two MagnaClean® filters were installed to clear the heating system from sludge and debris, followed by a system flush. To create hydraulically separate systems from the new boilers to the existing radiator system, a plate heat exchanger has been installed. This not only divides the primary and secondary circuits, but also ensures a highly efficient heat transfer with minimal losses between the two, thanks to the heat exchanger’s large surface areas. It also stops any dirt and debris from the secondary circuit entering the new boilers and pumps.
The complete plant room was fabricated and built off-site at Bunton M & E Services workshop, dismantled and delivered to site reducing the total installation time on-site to just four weeks.
Identifying the right output and matching heat demand
For the boiler installation, two Wessex ModuMax mk3 WM254/508V modular condensing boilers were chosen. This combination consists of two stacks with two boiler modules in each, delivering a total output of up to 1,016kW and a turndown ratio of 20:1. The turndown ratio refers to the ratio of maximum capacity to minimum capacity. In St Paul’s case, the boilers can deliver any output from 50.8kW up to 1,016kW. This ensures the load is matched to warm the building up, and in periods of low heat demand, the boilers are not constantly cycling and wasting energy. The modules can easily be stacked on top of each other and side by side to offer a variety of installation options. Backed up by a 10-year warranty, the space saving modular boiler, which fits through a standard doorway, provided the installation flexibility needed for St Paul’s Cathedral.
As the system was changing from steel shell boilers to condensing boilers, modifications to the flues were required. Robin comments
“You have to be very aware of the structure of the building as you cannot change anything without permission. A FuranFlex flue liner was specified by Flues UK and installed down the length of the 100ft rain water chute into the plant room.”
The flue liner was installed to meet the needs of modern condensing gas boilers which meant ensuring pressure and water tightness, as well as providing protection from the condensate which can cause corrosion due to its slight acidity of typically 3.5pH.
Meeting hot water requirements
Due to the popularity of St Paul’s Cathedral, the summer months are a challenge in terms of hot water demand. Coach parties arrive at the cathedral and use the facilities such as toilets and catering at the same time in a relatively short period, causing an extremely high peak demand. Two Hamworthy Powerstock PS500 glass-lined calorifiers with a capacity of 500 litres each and a recovery time of 18 minutes were chosen to meet the requirements. The heat to the indirect fired water heaters is supplied by the Wessex ModuMax mk3 boilers.
“The Powerstock calorifiers have a quick recovery to cope with these peaks in demand. We had to install two 500 litre models, as we couldn’t get the larger 1,000 litre model into the plant room.”
The cathedral has already felt a significant change from the time prior to the installation of the new boilers.
“The speed of heat up has greatly improved. Previously it would take a week to heat the cathedral up from cold, but now it only takes one day, the heating runs 24/7 on weather compensation.”
Weather compensation means a small outdoor sensor is fitted to adjust heating controls according to outside temperature changes to ensure more efficient operation of the heating system.
Ticking the boxes of a successful project
The challenge to provide an energy efficient and compact heating solution to be fitted to an old heating system without changing St Paul’s Cathedral’s building structure was successfully met. Space restrictions were overcome by choosing a modular boiler system to allow installation flexibility and access. Thanks to multiple water heater sizing options and their quick recovery time, the peaks in hot water demand in a short period of time were met whilst taking plant room space into account.