Off-site benefits

07th July 2020

With off-site fabrication techniques predicted to surge in the next five years, we look at the benefits of off-site manufactured techniques for heating in schools.


Off-site is on the rise. According to a survey by legal firm Clyde and Co, two-thirds of the top 50 construction firms anticipate doubling the amount of work carried out off-site to improve efficiency, reduce costs, tackle the skills shortage and overcome technical challenges. With reports of 30% cost and time savings[1], tighter quality control and reduced waste, there are clearly big benefits to be gained from this process.


In the building services world too, use of off-site manufactured equipment is growing in popularity. When it comes to heating, it’s an approach that can deliver huge benefits on school refurbishment projects, from greater design flexibility to meet individual project and customer requirements, to time savings for increased ease of scheduling.


The bespoke rig system, designed to simplify multiple boiler replacement, is a case in point.


Improving the efficiency of the UK’s older school buildings – and the heating service – remains a major challenge for the building services industry. Replacing ageing boiler plant with advanced condensing boilers and adding the appropriate controls is still one of the most cost-effective solutions for schools to achieve significant energy and carbon savings.


In our experience, it can cut gas consumption and associated costs by as much as half, helping schools stretch their straitened funds further, while contributing to a more comfortable and, ultimately, more productive learning environment.


Summer shutdown

School boiler replacements are traditionally scheduled for the summer holiday period, as upgrading the heating system is typically considered only to be feasible when the site doesn’t require a continuous hot water or heating supply for an extended period.


While the summer shutdown may provide the perfect circumstances to carry out refurbishments from the school’s perspective, for designers, specifiers and contractors, it coincides with the busiest time of year. This can present a series of challenges. Firstly, contractor availability may be an issue. Secondly, where a number of schools require heating refurbishments within the summer holiday period, this puts pressure on the maintenance team to squeeze all the planned replacements into the tight timeframe.


So how does a solution like the bespoke, off-site rig overcome these issues?


The arrangement of the boilers achieves the aim for improved energy efficiency, for one thing. Replacing larger boiler units with multiple fully-modulating condensing achieves a greater turndown ratio, allowing the boilers to adapt to fluctuating heat demand for more efficient energy use and increased reliability. It also makes for easier future maintenance and uninterrupted heating provision.


Design flexibility

But that’s just the starting point. In older school buildings, access limitations and lack of available plant room space – in addition to tight, fixed installation schedule – are frequent challenges.


Using site-assembled manufacturer cascade options will simplify and speed up installation. However, a key benefit of the off-site rig system is that all project and site requirements can be addressed and resolved from the outset, at the design stage. Indeed, it’s this flexibility that is central to its success.


The bespoke rig is based on individual boilers from 30kW to 300kW output, with no limit to the number that can be incorporated. Designers can define the maximum and minimum output, the number of boilers and whether to use a back-to-back or an in-line layout.


They can also address any physical site restrictions through a choice of header extensions and connections. A further option to overcome access restrictions is for the bespoke rig to be designed to split into smaller modules, with simple re-connection into a single frame in the plant room.


The rig can additionally integrate controls such as weather compensation, sequencing or Building Management System direct operation to maximise seasonal efficiency for lower running costs.


Only once the design is clearly defined does production take place. This is carried out in a factory environment with quality-controlled end-of-line testing providing added quality assurance. The boilers are then delivered to site on a wheeled rig unit. As even the position and size of the system connections on the rig can be produced to match the existing system pipework in the plant room, it is ready for rapid, easy connection to the system.


Time and space-saving solution

So which schools are using this off-site technique? A recent example is Bridgemary School in Gosport, run by the Kemnal Academies Trust. When its two old pressure jet boilers needed replacing, consultant engineer Fred Edwards at Ridge and Partners LLP specified six Remeha Quinta 115 boilers on a wheeled rig unit to achieve the improved reliability and high efficiency required by the Trust.


In addition to the plant room space restrictions and tight schedule, the primary and secondary circuits needed to be segregated to optimise boiler performance and longevity. Installing the boilers on a bespoke rig met all these requirements.


“The bespoke-designed rig system provides a time and space-saving solution to boiler replacement,” said Fred, “making it easier to get the plant into small footprints.”


Early visualisation

Working with Ridge, Remeha prepared detailed 3D drawings of the layout. This early visualisation is particularly useful for schools where boiler replacements need to be approved by a number of stakeholders.


The drawings then formed part of a comprehensive operations and maintenance documentation manual for Bridgemary School, for simpler future servicing.


Plate Heat Exchangers (PHEs) are increasingly applied to achieve hydraulic separation between the boiler circuit and the heating circuit. At Bridgemary School, the PHE was selected by Remeha to meet the specified boiler output and temperature, and oriented on the rig to meet the consultant’s requirements for non-disruptive future servicing. Air-dirt separation was installed to protect the PHE from the older retained secondary pipework.


Integrated into the design are pumps specifically selected for the duty required for PHE operation, an expansion vessel, a pressurisation unit, and a dosing pot to ensure good condition water.


Installation in days

To shave further time off installation, the controls were pre-wired for faster connection to the new Building Management System control panel. “The bespoke rig was great,” said project contractor IDWE’s Paul Neve. “It was wheeled straight off the tail lift and into place, saving us a lot of valuable time.”


So what does the rapid changeover mean? With installation and commissioning able to be reduced to days rather than weeks comes greater planning flexibility. In other words, boiler replacements no longer need to be restricted to the long summer holidays.


Efficient by design

The benefits for schools from using off-site fabricated equipment are clear. But critically, the whole supply chain benefits from this technique.


For consultant engineers, the greater design flexibility makes it easier to meet all project and customer requirements. Added to which, there is full assurance that the specification has been met.


And as the bespoke rig system lessens the intensity of skills required on-site, it is easier for contractors to plan ahead and put these skills to use on other projects, thereby increasing site productivity. Hot works are also reduced, creating a safer environment for both installers and the school.


For schools striving to improve their energy efficiency, an off-site heating solution like the bespoke rig delivers at every stage of the project – from design and specification, to installation, commissioning and future maintenance. And thanks to its inherent flexibility, it scores top marks for quality installation and long-term efficient building performance.


This article first appeared in CIBSE Journal

[1] Rethinking Construction (The Egan Report) 1998