The refurbished Mailbox is claimed to be the UK's largest mixed-use building and is central to the city's regeneration plans. It has also been heralded by some as a blueprint for urban regeneration.
The new development includes two hotels, 200 luxury rooftop flats, 23 000 m2 category A office space, designer fashion shops, canalside restaurants and café bars, and secure car parking.
The residential scheme by Crosby Homes on the top level of the project is the brainchild of property consultants Alan Chatham and Mark Billingham. But while providing luxury homes, the residential scheme also created a challenge for engineers – how to cool the building. The flats are built into the existing roof, removing the area that would traditionally be used for plant, and as John Cornish, senior design manager with design and build contractor Crown House explains: "Air-cooled plant is too noisy so any building tenants must use water-cooled plant." This, he says, is part of the lease conditions.
A system was therefore needed which used neither air- cooled chillers or cooling towers. The solution involved "taking advantage of a naturally occurring phenomenon" enthuses Cornish.
When old site drawings were studied the developers found that a disused canal basin lay alongside the building. This was excavated by Crown House and found to be in good condition, despite having been filled in for over a century. This has been used to provide a waterfront area, but the water also serves a purpose in the building's air conditioning system.
The air conditioning infrastructure centres around a condensor water circuit that uses the canal water as a heat rejection medium. "There is a main circuit for the entire building," Cornish explains, "which each tenant then connects into." The canal water is pumped into the basement, where it is filtered before passing through heat exchangers and back into the canal, having been reoxygenated along the way. Discussions were held with British Waterways reports Cornish, and thermal modelling carried out to make sure that the water temperature would not rise by over 3° between extraction and exhaustion.
One of Mailbox's new tenents, for which Crown House carried out the fit-out of air conditioning plant, is Railtrack. Two Carrier Global chillers have been used to serve its 7432 m2 offices, where more than 650 employees now work. Each unit has a nominal capacity of 352 kW, and operates on 134a refrigerant.
The benefits of water-based air conditioning are considerable. Because water cooled units are more energy efficient than their air cooled equivalents, they are also more compact, requiring only 25% of the plantroom space.
The plantroom for the Railtrack installation is under 50 m2. Around 150 m2 of lettable floor area has been freed up by using the two Carrier chillers and the canal water ring main. As a result, the system should deliver significantly lower running costs combined with dramatically increased floor areas. And when, as is increasingly the case today in prestige inner-city developments, luxury flats are built on the roof, chillers installed internally are an ideal solution. A true gift indeed for Mailbox tenents.
Source
Electrical and Mechanical Contractor