Why do many highrise condominiums overheat in spring?

It has to do with the two-pipe heating and cooling system that is common in many condominium buildings, particularly older ones.

In these buildings, heating and cooling in the units is provided by “fancoil units.” As the name suggests, the fancoil unit has a fan that blows air over a coil. The moving air is either heated or cooled depending on whether the coil is filled with hot or cold water. The hot or cold water in the coil is fed from the building’s central plant.

These fancoil units have a typical thermostat that allows the resident to switch from heating to cooling, to adjust the temperature set point and, sometimes, to control the fan operation. While this thermostat gives the impression of complete control, the situation behind the scenes can be another thing altogether.

Many buildings have what is known as a “two-pipe” system. With this type of system, the central plant can provide the suites with either heating or cooling but not both at the same time. In winter, the water in the pipes serving the coils is heated by the boilers; in summer, it is cooled by the chiller and cooling tower. Changing over between these is a costly exercise and takes some time.

The condominium board has the uncomfortable task of deciding when to change from heating to cooling in spring, and from cooling to heating in fall. Most do this by defining a changeover date at each end and then sticking to it, no matter what happens outside. However, spring invariably brings some unexpectedly warm days before the changeover date. With no air conditioning available, the building overheats, causing discomfort and complaints, especially from residents on the south side of the building who pick up heat from the sun. They think the board is crazy to stick to their fixed date and advocate for an accelerated changeover.

However, if the board had decided to changeover earlier, a couple of frosty – 5 C nights would have occurred, causing everyone to be cold, particularly the folks on the north side of the building.

The lesson is to be patient. Changeover will never be done at the perfect time but it will be done. Understand this is not just the flick of a switch like it might be in a home; there is a significant investment made to changeover from heating to cooling.

Sally Thompson, P.Eng., is executive vice-president and national practice leader for property condition assessment services at Halsall Associates. She acts as project principal for a wide range of capital planning and restoration projects for a variety of building types. Sally can be contacted at sthompson@halsall.com.