Earlier this year we were invited to provide a costed design solution for a new boiler plant at St Johns Church, Tunbridge Wells.

St Johns, Amherst Road, Tunbridge Wells, Kent

A large, Grade II listed building, probably the largest church in the area, it comprises an enormous high ceiling worship space, with the addition of vestry and offices.

Edwardian postcard of the interior
More recent view at an event

The church building management team knew pretty much what they wanted to achieve, helped by their professional engineering roles in the electrical power industry.

Existing gas boiler cascade 150Kw

We found a cascaded set of three commercial 50Kw cast iron Ideal atmospheric boilers. The Church technical team had previously fitted a BMS (Building Management System) that allowed them to set heating temperatures and this also did a basic weather compensation function.

The Church’s BMS was retained, as it was relatively new and did everything they wanted

There was an ability to use one of the boilers to heat the administration areas separate from the large church when required, but this had been piped in a way that meant it was going to have many more ‘run hours’ than the other members of the cascade.

Let the dismantling commence

The boilers were starting to show their age, and a couple had begun to show signs of ‘back end corrosion’ where the continual cold warm ups had created condensation based corrosion issues over the years.

We’ve got to fit all these boxes in the boiler room, and there’s more to come
Unexpected hole in floor under the old boilers. Just shows you can’t plan for everything.
We worked late – cleared out the nearest three Screwfix branches of fibrous screed – so we could start on a flat surface in the morning

Ideally the new boiler plant would be able to run in weather compensation mode via their BMS, which was used to minimise energy wastage, while allowing the heating schedule to be planned remotely, and also to facilitate zoned heating of the office accommodation.

Mixture of commercial and domestic circulators here, the separation between the office and main church was a bit Heath-Robinson

Our proposal, working with their team, was to separate the office and main church boiler plant, as these are used in very different ways.

New plant assembly underway. The item nearest the camera is the Viessmann cascade header, this blends the outputs of the three boilers and separates their flow requirements from those of the load (ie: the Church).

We suggested using our favourite light commercial solution, the Viessmann 200W, which is a heavyweight stainless steel wall hung boiler – and use a cascade rig to link three of these together on a single flue header. Fortunately the existing chimney was just large enough to fit a new stainless lining system inside.

Scaffolding up
Chimney needs work before we can finish our part
View to the car park
The flue liner is now in!
Flue connection detail in the boiler room

The new boilers would be linked to a Viessmann 300K control unit, that would sequence, rotate and load share the boilers. Our customers at St Johns would use their BMS to send a ‘flow temperature’ requirement to the Viessmann cascade, and this would make its own decisions on how many boilers to use, and at what power output. In essence, this gives a variable power output of between 10-150Kw.

Ricky demonstrating Viessmann 300K boiler sequence module

In practice this will mean that for a heating request, three units will fire up and as the building temperature rises, the number of boilers used will reduce.

We competitively tendered for this work, and were awarded the contract.

Our proposal included a Mikrofill automatic filling device, and a dosing pot. The dosing pot allows the church staff to monitor the radiator water quality and add chemical dosing easily when required.

MikroFill auto filling device and modified wiring in plant room

The management team were concerned about dirt in the system, we recommended the use of a SpiroTrap commercial magnetic separator. Unfortunately, having decided to exercise their option for this around 4 weeks before start date, we found there was a 2.5 month lead time for these items, none were available in the UK. In the end, a new old stock DN65 unit was found on eBay, which worked out very well as it was indeed unused, and in as new condition.

2.5″ bore Spirotrap flanged magnetic dirt separator

Moving on to the offices, some new pipework and radiators were needed here. We fitted a Worcester Greenstar 4000 combination boiler, spaced on a Unistrut frame to avoid a damp wall, to carry out the office heating functions. This has been augmented with Honeywell Evohome zoning, so that there are six separately addressable areas.

New Worcester 4000 on Unistrut frame

Both the main church BMS, and Evohome, can be scheduled from the internet or on site at their respective control panels.

Administrative area Evohome zoning off Worcester 4000

Our scaffold contractor got us to the top of the church chimney, where unfortunately we found significant structural deterioration at the top, which not unusual, and is undetectable from the ground. The church brought in their stonemason and an excellent repair was made.

Flue system finished, stack repaired and scaffolding removed (September 2021)

A large bore liner was installed by us, having been designed by our flue supplier, linking to the Viessmann flue header in the boiler room. An access panel has been put in place to inspect the transition from flexible to rigid flue at the very base of the chimney.

Worcester boiler fitted with intelligent filling accessory

The boilers were supplied by us with a full Viessmann 10 year warranty (yes, on a commercial boiler plant) and we also arranged Viessmann commissioning, which went without a hitch, the commissioning engineer being very complimentary on our work.

Test and Purge points fitted to gas supply. Gas press fit used on this job.
Rick and Brad almost finished

The Worcester Greenstar 4000 was also supplied with a 10 year warranty; it also has the Greenstar intelligent filling option fitted.

The St Johns Team were very supportive, and of course, they had an unusually good technical appreciation of what they wanted, so working with them, the installation came out on time, and on budget!

This is our third Viessmann commercial ‘up a chimney’ job in 2021.