McCarthy Stone is the UK’s leading developer and manager of retirement communities.
A developer building new homes for social housing and for private sale.
The developer planned to build eight homes in a village on the outskirts of Oxford.
Five of the homes were three-bedroom houses with two full-sized storeys and the third bedroom in the loft. The other three were bungalows that could be configured with two bedrooms or with a single bedroom and a study.
The brief to keep the build cost low raised a common dilemma in construction. Modern building materials are very efficient at preventing the loss of heat from a building in two ways:
The building regulations mandate a minimum standard of insulation and a maximum allowable air leakage but the highest quality construction materials offer a substantial improvement on those standards. However, improvements in the thermal performance of building materials correspond with increases in not only the price but also the embodied carbon: the carbon emissions produced in the manufacture, assembly and ultimate disposal of those materials.
The developer's brief was for Atamate to deliver building services that would deliver comfort and energy efficiency without requiring the most expensive building materials.
|Eight newly built houses
|atBOS controlled systems
|atBOS data products
Demand controlled ventilation
Exhaust air heat pump
Atamate's approach was to make the most efficient use of the low-carbon electricity provided by the national grid. All building services were electric, which delivers much more carbon-efficient energy than mains gas. However, electricity is more expensive than gas when calculated per unit energy so cost efficiencies were delivered using an extensive control system.
The principle underlying the heating was to use fast-response electric panel heaters under occupancy control.
The homeowner could use the user interface to choose the temperature setpoint and could vary that setpoint according to the calendar controls. For example, someone working at home is likely to prefer a room warmer than someone sleeping under a duvet.
The heat was provided by electric panel heaters which could quickly warm a room when atBOS detected occupancy but switch off immediately when someone left the room. A 'boost' function allowed occupants to increase the setpoint for a pre-determined time period, allowing some manual control over their home's heating.
Because the building fabric was designed to minimise air leakage, the homes needed a ventilation system. Placing the ventilation under atBOS control maintained air quality but avoids ‘over-ventilation’, in which a ventilation system sustains an airflow even when the air quality is high. Over-ventilation wastes the energy needed to power the extractor fan and also because incoming air needs to be heated.
The principle underlying the ventilation design was that air should enter the homes through the bedrooms and living rooms, which typically have the highest air quality, then pass through the home to the bathrooms and kitchens where indoor pollutants are often produced, and out of the house through exhaust vents.
By using ceiling sensors and valve-controlled inlets in every room, atBOS controls ventilation on a room-by-room basis which keeps the airflow, and the need to heat incoming air, to the rooms where ventilation is required.
The ceiling sensors measure humidity, carbon dioxide and volatile organic compounds and only ventilate a room if one of those parameters fall below a pre-defined setpoint.
The inlet valves are closed when air quality is high, which prevents air leakage that increases the heating load. When a bedroom or living room needs ventilating, atBOS opens the inlets in that room only. If it’s the kitchen or bathroom that needs ventilating, atBOS opens inlets in the room with the lowest air quality, pre-empting a need to ventilate that room later. In either case, the inlets ensure that ventilation is directed through the rooms that need ventilation rather than maintaining airflow through the whole house.
Once atBOS was installed in the homes, it became cost-effective to place windows and fire alarms under atBOS control even though it would not have been worth installing atBOS for those services alone.
All of the three-storey houses had rooflights in their loft bedrooms. The rooflights improved the lighting and ventilation in those rooms but were difficult to access. Motorising those windows and placing them under atBOS control allowed them to be opened or closed through the user interface.
Controlling the rooflights enabled atBOS to use them for purge ventilation, which was sometimes required during the summer. If the indoor temperature was uncomfortably hot while the outdoor temperature was lower, opening the rooflights allowed the hot air to rise out of the house while opening the ground floor ventilation inlets allowed outdoor air to replace it.
All eight houses are fitted with a standard fire detection system of smoke detectors and kitchen heat detectors. Integrating the fire alarms with atBOS ensures that if the fire alarm is ever triggered, atBOS will activate escape lighting that ensures routes out of the houses were well lit.
If the home was empty when the alarm went off, atBOS sent a text alert to the designated owner and anyone else specified on the user interface. They were then able to contact the fire brigade even if no one is at home at the time.
In newly built homes with well-insulated fabric and efficient space heating systems, the largest single energy demand is usually for hot water.
These homes used the Ecocent boiler, manufactured by Earth Save Products, to heat water as efficiently as possible. The Ecocent supplements mains electricity with an exhaust air heat pump which extracts heat energy from the ventilation duct, capturing energy that had been used for space heating and would otherwise be expelled from the home.
Placing the heating and ventilation under atBOS control delivered a high level of energy efficiency without compromising comfort or requiring the most expensive building materials, which kept the sale prices at an affordable level.
All eight houses have now been sold and although Atamate has not conducted a post-occupancy evaluation, they are configured in a very similar way to the Cogan Terrace development that has been the subject of intensive study and revealed that the configuration delivers an extremely high level of energy efficiency, comfortably meeting the standard of 15 kWh/m2/yr for space heating recommended by the UK government's Committee on Climate Change.¹
Using atBOS allowed that standard to be met without needing the highest level of insulation available, with its associated high cost and high embodied carbon.
¹ Committee on Climate Change (2019) UK housing: Fit for the future? 135pp. https://www.theccc.org.uk/publication/uk-housing-fit-for-the-future/