Cool comfort: alternatives to air-con

Top-end flats now have air-conditioning. Chris Partridge looks at the alternatives

As Britain sweltered in the heatwave, tenants at the top end of the market were beginning to demand air-conditioning. Some agents have lost tenants purely because the flat or house isn't climate-controlled, and if such hot summers continue - as seems likely - this issue won't go away.

Letting agent Virginia Skilbeck of Douglas & Gordon in Chelsea has already lost tenants because of this. "We had a tenancy fall through in Ennismore Gardens even though the applicants, a Spanish couple, desperately wanted to rent the flat," she says. "It is a purpose-built block, so they just assumed it had air-conditioning. When they found out it does not, they instantly pulled out."

Growing demand for air-conditioning puts landlords in a quandary, Skilbeck believes. One option is comfort cooling, a system that pumps cold water through a heat exchanger and blows the cold air into the room.

Comfort cooling is inefficient and consumes just as much energy as air-conditioning, but it is easier to install in period buildings. "We are handling a refurbished listed building in Chelsea where they managed to get comfort cooling in, but there are problems with noise so they've had to install soundproof doors," Skilbeck says.

Air-conditioning is becoming the norm in new top-end developments, says James Hyman of Cluttons in Tower Bridge. "A lot of high-value people only buy in buildings where some form of air-conditioning or comfort cooling is provided," he says.

The intense heat of July pushed air-conditioning to the top of the list of essential features for many buyers, Hyman says. "It is no coincidence that the two air-conditioned apartments we had on the market for sale in Tea Trade Wharf, one at £1.4m and one at £860,000, went under offer during the heatwave," he says.

Environmentally sensitive landlords do have options, however. New building techniques can make air-conditioning and comfort cooling unnecessary. Super E, a system from Canada, is designed to slash the energy use of the average house. A Super E house is heavily insulated and almost air-tight. Air is circulated by a blower and heat exchanger, so incoming air is heated by outgoing air.

Researchers in north Japan, which experiences bitter winters and searing summers, measured the temperature variations inside a Super E house. In winter, it never fell below 16C inside even when the heating was switched off overnight, when temperatures reached minus 14C. In summer, inside was a comfortable 27C on 36C days.

Then there's the thermal mass approach championed by Bill Dunster Architects, designers of the BedZed development in Wallington, Surrey. The cowls on top of the building turn into the wind to draw stale air out of, and fresh air into, the flats. The heavy concrete structure acts as a heat store, or thermal mass. In summer, it keeps residents cool by absorbing heat during the day and radiating it out again at night. In winter, the process helps keep the flats warm. "It is like a cathedral or a cave; it stores heat," says Steve Harris, a senior architect at Dunster.

Heat input from the sun is carefully controlled by the position of the windows, walls and canopies. The high summer sun does not penetrate inside but the low winter sun shines through the windows and heats the concrete floors and walls.

The thermal mass system and the cowls are working well, and residents say they have had no need of air-conditioning. The hi-tech combined heat and power system is still not working, but that's another story.

Estate agents Savills studied resale values at BedZed and came to the conclusion that, allowing for the relatively large size of the units, flats in the development command a premium of up to 20 per cent compared to similar but less environmentally sound developments.

The lack of air-conditioning does not seem to be a brake on lettings in "son of BedZed", a small block called BowZed in Tomlin's Grove, London E3, built by the developer Yorklake. The ziggurat shape maximises the sun's rays and cowls at the top circulate air. A two- bed flat there is available to let with Foxtons (08454 563 335) at £350 a week.