What are the options to reduce waste in FCU design at the Cat A stage?

Fan coil unit (FCU) waste is often generated in a commercial building when the initial basic functional fit out, known as Cat A, is superseded by a second fit out, referred to as Cat B. The second fit out takes place when the premises are rented out to tailor the space to meet the business needs of the incoming client. 

Waste is generated where FCUs that are either no longer in the right place, or are now oversized for the altered space, are removed, and replaced, often by an increased number of smaller alternative FCUs. As well as generating waste, this practice adds additional cost and time to the project’s Cat B fit out. The options to reduce this FCU waste at the Cat A stage range from:

• Trying the eliminate the need for a second fit out in the whole building by going straight to Cat B when a client for the space has been found
• Having a halfway house approach where some of the floors of the building are fitted out at the Cat A stage and the rest are only fitted out to Cat B once the floor is rented
• Using larger quantities of smaller FCUs at Cat A stage
• Using adaptable larger FCUs that can be kept in position and more easily adapted to match new layouts  

In this blog we will look at each option in turn to investigate its viability and feasibility for the building owner and the Mechanical and Electrical (M&E) designer.

RICS estimate that 11 percent of UK construction spending is on fit outs. Therefore, finding the best option to reduce waste at the Cat A FCU stage would generate cost savings and help to reduce UK construction waste which stood at a total of 59.1 million tonnes in 2020. Options on ways to reduce FCU waste during fit outs are covered in our white paper ‘Reducing waste in development fit outs through effective fan coil solution design’. It shows how designers and specifiers can make decisions at the Cat A stage to maximise the flexibility of fan coils and minimise waste at subsequent fit outs.  

What are the four possible Cat A strategies that could be employed to reduce fan coil waste? 

There are four options that could reduce fan coil waste and they either look at different planning strategies or technological solutions to have a positive effect on project waste and capital costs:

Go straight to Cat B design

This requires a lot of cooperation at the design stage and is only viable if the final client for the building is known. It may be possible where, for example, a large corporation either decides to construct, own, and use a building or guarantees that they will move into a building on a long-term lease. Although this happens, it is rare and not without problems, as the Cat B specification needs to be set in stone quite early in the project. This means that any design alterations required by changes in the strategy, structure or size of the company can create issues of their own if not carefully managed.

Adoption of a ‘halfway house’ strategy

On large scale projects, one option that could be considered is to fit-out and market only a limited number of Cat A floors. The idea is that other floors could then go straight to Cat B once tenants are secured. This reduces the potential for waste generation when going from a Cat a to Cat B fit out, however, it does sacrifice the economies of scale that are possible when fitting out all the floors to Cat A at one time. 

However, such an approach creates additional coordination and a planning consideration as the building will be operational. Going straight to a Cat B fit out also requires all the pipework, ductwork and wiring to be fitted from scratch, meaning that the tenant has a longer wait before they can get up and running. This may deter some clients for whom time is of the essence and they may prefer the choice of the adaptable FCU strategy, where their Cat B requirements can be more swiftly delivered.

Use smaller FCUs

The use of more, smaller FCUs, instead of fewer, larger models, is an option that would reduce waste. However, whilst it would reduce the chances that adjustments to FCU strategy would be required at the Cat B stage, this increases the cost to the building owner not the tenant. Every extra FCU needs a controller, a valve set, and pipework and electrical connection on top of the cost of the unit itself. Although smaller FCUs will make the property more attractive and easier to lease to prospective tenants, the upfront cost associated with purchasing and installing more FCUs may be hard to justify in the owner’s project business plan.

When asked for his view on the use of smaller FCUs at the Cat A stage Sam Smith, Associate Director of Building Services at WSP said: “We see issues with structural coordination when working with an increased number of units or a notionally agreed reduced zone/bay. There is also an increased spend associated both with the extra valve sets, condense runs and connections needed, and with any additional secondary distribution from the smaller FCUs required. So, although potentially beneficial in the long term when compared to a typical Cat A, this option comes at cost and with its own challenges and restrictions”.

Use adaptable larger FCUs

There are larger FCUs that are designed to be able to be compartmentalised to service the requirements of up to four separate spaces. This means that they can satisfy the needs of the open plan Cat A fit out and be easily adapted to meet the more complex requirements of a Cat B fit out. This is facilitated by ducting running from the adaptable FCU into the spaces to be conditioned and each room has separate controls to ensure that the FCU meets the individual needs of each space. This set up should not be confused with a larger FCU that has more than one duct running into separate rooms but there is only one control. All the rooms get the same conditioning regardless of their requirements. This can lead to either overheating or over cooling rooms that have no control over the air temperature from the FCU. 

The extra ducting between rooms required for adaptable FCUs is sometimes anticipated to be an acoustic issue with the potential for talking from one room to be heard in another. However, there is very little risk of this happening, as has been demonstrated by acoustic testing of the systems. The only other additional design element that may need to be considered when using adaptable FCUs is the need to fit a separate small duct to supply fresh air. This is required if the central FCU turns off the fan in an area when the required condition has been reached to ensure that a supply of fresh air is always available.

These adaptable FCUs present a real opportunity for M&E designers to produce a specification that can reduce technology waste not just for the first Cat A to Cat B transition but also for all the ones that will follow, as tenants leave, and new leases are agreed. That can add up to a significant saving in cost, time, waste, and carbon emissions and make the choice of these FCUs an efficient and sustainable design solution. For a Cat A fit out to reduce long term technology wastage it needs to, as far as possible, build in flexibility when choosing FCUs to overcome the changes that will occur in the building once a Cat B fit out has been completed.

Where can I find more information on the best options to reduce fan coil waste at the Cat A stage?

More information on how to create designs that minimise fan coil unit waste is contained within our Ability white paper ‘Reducing waste in development fit outs through effective fan coil solution design’ that is available to download. If you would like to learn more about how adaptable fan coils  can be employed at the Cat A stage to help reduce waste in FCU design, please contact our experienced team who will be happy to help advise on the options suitable for commercial projects.

Troy Chambers