Case study: Meeting the challenge of energy efficiency

How heat recovery and intelligent controls combine to meet stringent efficiency requirements at a private medical clinic in London

With the introduction of ever more stringent energy efficiency standards and legislation, building managers need to remain constantly vigilant about how to reduce carbon emissions. However, today’s climate control systems are already highly energy efficient, so the debate has grown to cover how we should cut usage as well as increase energy efficiency.

The Government’s fourth carbon budget announced earlier this year - which requires the cutting of emissions by 50% from 1990 levels by 2027 - means that the installation of the latest energy-efficient climate control systems is no longer sufficient to meet the nation’s carbon reduction targets. Building managers and owners also need to focus on ways to monitor, control and reduce everyday energy usage as a means to achieve these legally-binding objectives.

Non-critical areas are fitted with a total of 15 RTD-NET controllers

However, embracing a policy of controlling and cutting energy usage is an approach that also offers huge money saving potential. But the question is: how do we encourage end users to cut back on the amount of heating and cooling they demand, when it is widely acknowledged that changing user behaviour is the holy grail of achieving real carbon reduction?

One example of how energy savings can be achieved in this way is at a private medical clinic in London, which recently underwent refurbishment. Here, a combination of highly-efficient VRV heat recovery and the latest generation of intelligent building management controls were used to provide the best possible energy efficiency and to overcome a number of practical challenges for the engineers.

The clinic is housed in a 200-year-old six-storey Georgian Terrace in central London, with no access to the mains gas supply and a relatively limited maximum electrical demand. These factors, together with stringent external noise restrictions and a limited ceiling void space meant that, as consultant engineers, Arup, was required to specify a climate control system that was highly energy efficient and could meet the unusual demands of the project.

With the introduction of ever more stringent energy efficiency standards and legislation, building managers need to remain constantly vigilant about how to reduce carbon emissions

Part of the remit of the project was for fresh air handling and so two Daikin VRV III Heat Recovery Systems were specified, in conjunction with four Daikin VRV heating hydroboxes and a Daikin/Biddle Air Curtain, all of which use heat recovered from the building to provide warm air at the entrance to the clinic and to the clinical fresh air supply. Additionally, specially-adapted Daikin RTD-20 Control Units were used to help ensure the temperature inside the building stays at exactly the right level to keep staff, patients and visitors comfortable.

Two Daikin VRV III Heat Recovery Systems were installed for fresh air handling

Although based in central London, the healthcare facility, which includes basement and ground floor levels as well as four further floors, is not connected to the mains gas supply and this, coupled with a limited electricity supply, meant that electrical consumption needed to be kept to a minimum. In addition, to prevent condensation in the building, the inside air temperature was required to fall no lower than 14°C. Given the age of the building, the thermal insulation characteristics fell short of those expected from a more modern property, and therefore the clinic required a heating function through the night during the winter months. Any improvements to the thermal insulation would have impacted internal space, which the client was keen to avoid. However, this night-time heating provision was further complicated by the extremely stringent noise restrictions in the area, which are some of the strictest in the country for an urban area.

The two Daikin VRV III heat recovery outdoor units were placed in an acoustically-insulated plant room, each system serving different parts of the building. These supplied reclaimed heat from solar gain, lighting and densely occupied parts of the building to both the Air Handling Unit and the Biddle Air Curtain, which provides hot air at the clinic’s entrance. Air curtains normally place large load requirements on the electricity supply, but, as this model uses reclaimed heat whenever it is available, this is not the case and so it was ideal for this project.

As the VRV systems could not be run at night, due to the noise restrictions, duct-mounted electric heaters were used, controlled by custom-programmed RTD-20 controllers, which allowed the indoor fan units to come on when required without employing the VRV system.

Ryan Dunne, consulting engineer at Arup, said: “We were unable to use gas boilers on this project and the electrical load capacity would not allow us to use an electric system, so we opted for a low temperature hot water system that utilises the Daikin VRV system for heating and incoming air.

“The extremely tight planning conditions on noise meant we couldn’t run the VRV system at night, but we needed frost and condensation protection. The architect was also keen not to have electric panels on the walls and opted to install duct-mounted electric heaters for night-time use. In addition we were required to provide clinical-standard ventilation in part of the building and therefore didn’t want fan coil units. However, we were still able to use the VRV system for heating and cooling coils in the Air Handling Unit.”

Integral to the energy efficiency of the system is the use of 40 RTD controllers. These work individually to control each electrical heater, ensuring that the minimum amount of energy is used to provide precisely the correct temperature at any time.

Embracing a policy of controlling and cutting energy usage is an approach that offers huge money-saving potential

Dr Richard Fargus, whose company RealTime Control Systems worked with Scott McGavin of Daikin UK to devise the RTD range of controls, said: “The custom programmed RTD-20 Controllers offered a unique advantage to this project. They took control over the temperature protection function. One was placed in each consulting room to take control of the electrical heaters. Because each works independently they result in a highly-efficient system. Only a small uplift in cost is required to fit a controller to each heater, which negates the need to install a secondary climate control system, in order to achieve the desired outcome. This way the electrical heaters are totally interlocked with the climate control system.”

In total 19 custom-programmed RTD-20s were used in the critical areas of the clinic. In addition standard RTD-20s were used with the air curtain and in the dx coil, while non-critical areas were fitted with a total of 15 RTD-NET controllers.

These devices communicate to a Trend BMS system, creating a micro BMS at a local level within the building. This reduces the need for programming and met the client’s needs at a significant cost reduction compared with installing a secondary system.

Dr Fargus continues, “The RTD-20 is a scalable plug and play solution designed to reduce energy consumption. It was originally developed for retail environments where conventional controls are too expensive for small outlets. This solution utilises distributed intelligence, where each unit works independently, which makes it more reliable than centralised BMS and ensures that the hardware cost is always proportional to the energy savings achieved.”

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