When it’s time to think big
There’s a powerful environmental and economic case for underfloor heating in large spaces, says Mike Lamb.Underfloor heating is the greenest and most cost effective method of providing a comfortable working environment. These advantages are more apparent when large spaces are heated by underfloor systems that are part of a wider programme of intelligent design and sustainable-energy solutions. By choosing underfloor systems for major indoor spaces, building owners and specifiers can ensure a lasting solution and a possible ‘A’ rating for building efficiency. Energy saving
When underfloor systems are powered by high-efficiency gas-fired condensing boilers, energy savings of around 30% are possible compared with other methods of heating. This is because the underfloor piping grid spreads the heating effort over the entire floor area — creating a uniform, comfortable temperature with the heat concentrated at floor level, where it is most needed. An underfloor heating system requires water at lower temperatures than radiators, so condensing boilers can operate at optimum efficiency. Renewable energy
Heating large spaces using underfloor heating becomes even more attractive in energy saving terms where the primary heat source is a more sustainable solution such as a ground-source heat pump or an air-to-water heat pump. Both types economically and efficiently convert free natural energy into useful heat. Air-to-water heat pumps offer 350% efficiency or more, converting 1 kWh of electrical energy into 3.5 kWh of heating energy — even when the outdoor temperature is 0°C. In a well designed system, a number of heat pumps in a modular arrangement will ‘kick in’ one by one to match the demand for heat, but a relatively small boiler is usually installed to provide occasional thermal top up in the coldest periods. Heat-pump technology also enables an underfloor water system to double as an efficient cooling system during the warmer months, giving it a significant advantage over most other space-heating systems. Most systems in large commercial buildings that we have worked on recently operate in cooling mode for more months than in heating mode. The real potential of underfloor temperature management is realised when it is part of a sustainable systems programme, along with lighting and ventilation, under an integrated control system. This ensures that the components work together, rather than in opposition, and it can also allow zonal control to avoid, for example, unnecessary over-heating of office space out of normal hours. Ideally, all features should be in a building designed to maximise the use of natural light and minimise the loss of heat through doorways or windows. The current fast-growing demand for underfloor systems — especially for large spaces — reflects the view that traditional heating systems simply waste energy and do not provide an acceptable comfort level throughout the workplace. Radiators and other point-source heaters distribute warmth by convection currents — encouraging both draughts and hot spots. Worse, they circulate allergens, dust particles, fumes and germs — often creating an extremely unhealthy atmosphere. Because these heat sources are small compared to the space they are heating, they require high energy inputs if they are to make any worthwhile impact.
Heating for the 83 500 m2 factory of Airbus at Broughton in North Wales is provided by a Warmafloor underfloor system, which can be zoned according to production requirements
An excellent example of the benefits of underfloor heating, and one of the largest systems in the UK, is in the 83 500 m2 Airbus factory at Broughton, North Wales, where wings for the new A380 aircraft are assembled. Comfortable ambient temperatures of 18°C are maintained in deepest winter by pumping water at 50°C into the heating grid. This is calculated halve the heating energy requirement by 50%, compared to alternative heating methods. The Airbus system was designed, supplied and installed by Warmafloor. It uses 60 km of 20 mm polybutylene pipe and specially manufactured manifolds. The pipes are laid in each of the six equipping bays, and each bay has 10 heating zones. The zonal design enables heat to be concentrated in areas of the building being used for production at any one time. Hot water to each zone of an underfloor installation is controlled either by manual valves on the manifolds or, more usually, by electric actuators driven by remote thermostats or sensors coupled to an energy management system. Underfloor heating is an integral part of my own company’s head office, warehouse, and the newly opened sustainable-energy centre, which showcases the complementary energy saving offerings of 16 other like-minded manufacturers. The complex delivers optimum sustainability through intelligent combination of 12 simple, cost effective elements and, as a result, requires only 20% of the operating energy consumed by a similar conventional building. We believe this extraordinary sustainability performance will enable our building to achieve an ‘A’ rating when the proposed system for rating the efficiency of buildings is introduced. Cooling
To heat and cool our building at Fareham, we have two ground-source heat pumps, fed by 4 km of brine pipe ‘slinkies’ in relatively shallow trenches under the car park and one air-to-water heat pump, providing year round maximum controllability of free energy. Cooling accounts for most of our total energy demand — and the heat pumps meet all that demand by serving underfloor coils, chilled-ceiling coils, and further coils in the air-handling unit of our ventilation system. The heat pumps also provide almost all the heating energy, with the result that the gas condensing boiler is used for only two or three weeks a year. Solar panels can provide all our hot-water needs in summer and up to 25% in winter, even on dull days. A simple electric heater tops up DHW when required. The building is currently being monitored independently by BSRIA. For more details see www.sustainableenergycentre.co.uk Sustainability will be a major consideration in building and services design for many years to come. We recommend that heating specifiers should always consider the most sustainable energy sources and systems, to reduce costs and minimise environmental impact. Payback will surely be calculated not just in energy savings, but in the increased value and yield of ‘A’ rated buildings demanded by responsible owners and tenants. Mike Lamb is managing director of Warmafloor (GB) Ltd.