Listing buildings
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.
Output and 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.
Project challenges
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.
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. Robin elaborates: “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.”
www.heatingandventilating.net
Two Wessex ModuMax mk3 WM254/508V modular condensing boilers were installed at St Paul’s Cathedral Noticeable improvement
Ticking all the boxes
The cathedral has already felt a significant change from the time prior to installation of the new boilers. Robin says: “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.
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.
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 for the St Paul’s Cathedral project
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