Tony Millard, UK sales and marketing director, Carrier Air Handling Units, reveals the technical details that differentiate the latest Carrier advance in the UK air handling unit market
The new Carrier 39HR Airosmart Heat Recovery Unit has been dubbed the energy saver by its Dutch production team. This style of unit is a new venture for Carrier. It is an off-the-shelf air-handling system, which makes heat recovery standard even at the smallest unit size.

There are now many applications in the UK that will consider the application of air handling units that might previously have settled for other types of air conditioning, accompanied by mechanical ventilation or maybe just normal building leakage of air.

Schools, sports arenas, clubs, canteens, larger surgeries and health centres are particularly important building types in this regard. But the same applies to new studios and small offices too. What has changed? The answer is two-fold: the specification environment and the product designs.

Part L of the Building Regulations has many effects across this market. Centralised air extraction and trickle ventilation is no longer an acceptable strategy in terms of energy efficiency. Heat recovery needs to be shown to be taking place even in older public buildings as well as in new ones.

Fresh air has to be introduced to meet air quality standards. All new buildings are fairly airtight, so ventilation strategies are essential to avoid stale air and condensation. Efficient insulation means that buildings are also warm and so thermally efficient. Consequently, cooling is also likely to be needed for part of the year – so the specification process is complex. Air handling systems can now meet all of these requirements for both small and large buildings.

Previously, such a solution would only have been considered for larger buildings, probably only in the commercial sector. And then a specially designed unit would have needed to be commissioned if heat recovery was the key requirement.

The Carrier Airosmart and some similar products from other manufacturers can change all that. The Carrier product, however, differs technically in several ways. All the units in the new modular Carrier range have a small footprint, which will suit the applications referred to above. But it is in terms of heat exchange technology that the biggest change has been made from other so-called standardised products.

The smallest units – which cover airflows up to 1.3m3/s incorporate a counterflow plate heat exchanger rather than the more conventional crossflow exchanger. This can produce significantly improved energy efficiency values up to 90%.

For air flows of 1.7m3/s and above, a heat recovery wheel is used as standard. A sorption rotor is available as an option to allow the recovery of both temperature and moisture, increasing still further efficiency and energy savings. All these units can also be supplied with a complete bypass circuit allowing free cooling using outside air.

Integrating this facility can result in further significant savings in energy consumption.

The air flow in such a system is balanced.

The air handling unit introduces fresh air and extracts it – and uses both flows for heat recovery. The new Carrier system incorporates G4 Panel and F7 Bag filters as standard.

This enables it to filter outdoor air and provide a much higher level of air quality than traditional ventilation techniques. The filter types are compact and can be withdrawn for servicing from the side for maintenance.

The basic design is compatible with other Carrier air handling models and includes a high-quality double-skin construction. And it meets the following criteria when tested in accordance with BSEN 1886:

• Mechanical Strength: 2A

• Casing Leakage: B

• Thermal Transmission: T2

• Thermal Bridge: TB1

• Fire Class: B



With a UMP baseframe, the complete unit is designed to be transported and lifted in one section – therefore reducing the amount of sitework required.

At this level in the market, it is also thought to be essential that such units can be considered as plug and play, so they come complete with pre-wired controls. This makes it a convenient stand-alone product – a characteristic that the UK market has come to find attractive.

To increase still further the flexibility of this standard product, it is possible to incorporate a heating or cooling coil within the standard unit configuration rather than having to add it on or construct additional elements for the unit.

A further energy-efficient feature of the design is that it operates with electronically commutated brushless DC (EC) motors, which have been measured as using 15% less energy than the more commonly used asynchronous motors.

They are able to work efficiently at lower speeds providing an effect similar to inverter control.

Finally, this unit puts sophisticated heat recovery and controls technology in a standard off-the-shelf unit, which is economic to produce and sell. And, most importantly for customers, it is easy to select.

Despite its stand-alone capability, this product has also been consciously developed as part of the growing trend for integrated systems, and to meet increasing customer demand for energy saving options.

Even further energy savings can be expected for a building’s total carbon footprint in the case of the larger models if these units are integrated into a building management system.