Pressures to meet legal targets, improve fuel efficiency and reduce carbon footprints are driving the take-up of energy-recovery technologies

The government has set clear targets for all UK buildings to become carbon-neutral. New homes and new schools face a 2016 deadline, public sector non-dwellings are required to become zero-carbon by 2018 and other non-dwellings need to comply by 2019.

To reach these targets, the regulatory framework is changing to ensure contractors take positive steps to embrace low-carbon technologies on behalf of clients. Key strands of the Energy Performance of Buildings Directive (EPBD) are implemented in the UK through the Building Regulations Part L.

As far as ventilation is concerned, Part L2 covers non-dwellings of more than 1000 m2, Part L2A refers to new-builds and Part L2B covers existing buildings. Both sections refer to the Non-Domestic Heating, Cooling and Ventilation Compliance Guide as a means of showing reasonable provision for meeting the Building Regulations. Part L requires a maximum allowable specific fan power as part of the building services system to achieve Energy Performance Certificates (EPCs), which are now, of course, needed on the construction, sale or renting out of all buildings, apart from a few exempted commercial premises.

Ventilation has a critical role to play in delivering on this m&e sustainability agenda, and specifically demand-based energy recovery ventilation.

“Demand-based ventilation, typified by Vent-Axia’s Sentinel system, integrates proven control technologies and principles to respond to the exact ventilation requirements of a room at any one time, providing the right level of supply and extract airflow only when required,” explains Nygel Humphrey, industrial product marketing manager at Vent-Axia.

Sensor types – such as CO2, passive infrared (PIR), occupancy detection, humidity or temperature – are employed to determine the occupancy of the rooms and manage the system’s ventilation rates accordingly. They communicate with the main ventilation unit which, in turn, drives the fan to the required speed to deliver the airflow and respond precisely to room conditions.

Sensors can be combined to generate a hierarchy of control, and operation can be linked in to a building management system for control and monitoring.

“It’s logical to take this demand-based approach a step further by integrating energy recovery into the system,” says Humphrey.

“To that end we’ve developed Sentinel Totus, a demand-based energy recovery ventilation [D-ERV] solution incorporating the latest heat exchange technology.”

The performance of an integral high-efficiency counterflow heat exchanger is critical in raising the efficiency bar for D-ERV systems. Maximum energy is recovered from the extracted air (both heating and cooling in the summer) and transferred into the fresh supply air via the heat exchanger.

The D-ERV solution is suitable for multi-occupancy and variable-demand rooms, meeting the ventilation requirements of both new-builds and refurbishment projects. A typical application could include constant-pressure control to a network of hotel bathrooms, flats or apartments that require ventilation, but are only used for limited periods, usually morning and evening.

Periodical use

Alternatively, it could be used for control using CO2 sensors for school classrooms and lecture theatres that are only occupied during lessons by a variable number of students, but when used must keep CO2 levels within limits.

Equally, they suit office meeting rooms or open-plan areas that are used periodically during the day by a variable number of staff and visitors, but when occupied must meet required airflow rates.

The control principles employed in D-ERV technology also allow integration with associated space-heating and cooling systems in a building to generate further savings. Automatic air-conditioning and heating interlocks enable the system to optimise energy-recovery performance and provide free cooling during summer through optimisation of the automatic bypass control.

A user-settable night-time purge facility also helps reduce the start-up loads for a building’s air-conditioning plant or over-heat in summer from non-air-conditioned spaces.

D-ERV systems meet Building Regulations Part L2A and L2B requirements. They can achieve a specific fan power at 25% of designed flow rate, no greater than that achieved at 100% designed flow rate. This helps clients and end-users ensure their buildings meet European Union demands for the 20% cut in energy consumption by 2010 targeted by the EPBD.

“D-ERV systems only operate and consume energy when they have to. In many fixed-volume ventilation systems, the choice of control is limited to either on or off, with a fan speed set at minimum, medium or maximum. Rooms are often overventilated, or ventilated when empty or occupied by just one or two people,” says Humphrey.

There is plenty of interest in the role that renewable energies can play in reducing the carbon footprint of UK buildings. As a technology type, renewables are seen by many as a silver bullet because their use will score highly with EPCs and meet planning requirements (the 20% renewables target).

“With D-ERV technology, like Sentinel Totus, existing energy within buildings can be recovered and re-used, irrespective of how or from which source this energy was generated in the first place. This is true recycling which, ultimately, allows building occupiers to reduce consumption or even switch off mechanical equipment for longer periods.”

The drive towards energy efficiency promises significant opportunities for contractors. It also requires clarity of thought and purpose when it comes to making the right technology choices that will fit within the legislative framework and deliver long-term efficiency benefits for clients.

Originally published in EMC September 2009 as "The recovery position"