Healthcare
Safe heating in buildings
John Tarling, commercial manager Dunham-Bush, explains the importance of risk assessment when specifying LST radiators
Dunham-Bush commercial manager John Tarling
occupants, as is reasonably practical. Buildings such as schools, colleges, day centres, playrooms, surgeries, nurseries and care homes are used by people of all ages, who are vulnerable. Risk assessment, provided by the Management of Health and Safety at Work Regulations 1999, will enable the designer to identify hazards, assess the risk of injury and decide appropriate measures. All occupants are deemed to be at risk and some
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are more vulnerable than others to scalding or burning from hot surfaces or water temperatures. Research has shown that partial thickness burns to skin can be inflicted by solid surfaces at temperatures of 45°C or more for a period in excess of two hours (a possible occurrence if the occupant is rendered immobile or unconscious). Heating systems are typically designed using Low
Pressure Hot Water (LPHW) with a flow temperature of 80°C and a return temperature of 60°C. If the surface temperature of a heating device is between these two, then the average person could receive a partial thickness burn in about one second, with a full thickness burn being inflicted after approximately 10 seconds. Hence, a heating device should operate with a low surface temperature when achieving maximum temperature and running at design output.
NHS Estates Health Guidance Note ‘Safe’ Hot
Water & Surface Temperatures 1998 provides guidance for designers on safe surface temperatures of components and services. The guidance recommends that heating devices should have a maximum surface temperature of 43°C when operating under design conditions. Heating devices should be designed so that there are no surface ‘hot spots’. All openings (e.g. grilles)
24 May 2018
specifies the correct information that a manufacturer must provide from the test data and specifies how radiators and convectors are evaluated to conform to the standard. A radiator or convector can be tested to BS EN 442 and its thermal output can be measured at various water temperatures. This enables
afety is of paramount importance in all buildings and designers have a duty of care to eliminate or minimise all risks to a building’s
should prevent small hands entering the device and touching hotter surfaces inside the device. They should also be designed for easy access for cleaning and other maintenance routines to prevent dust and debris build-up and also to control infection. Consideration should also be given to exposed horizontal or vertical pipework within 2m of floor level, since this will present the same risk as the heating device. Pipework to the device should, therefore, be boxed or insulated. For most heating devices, the outlet grille has the highest surface temperature, but a risk assessment may deem the outlet grille does not present a significant hazard. Therefore, higher grille temperatures may be acceptable since casing temperatures will always be significantly lower than grille temperatures.
Standards for testing
CE marking of heating devices is a mandatory requirement for construction products and can only be applied to products that have been successfully tested to EU standards by a notified body, accredited under the Construction Products Regulations (305/2011/EU-CPR). The only accredited body in the UK is BSRIA, who test in accordance with these standards -
BS EN 442 Specification for Radiators and Convectors Part 1 2014 Technical Specifications and Requirements Part 2 2014 Test Methods and Rating Part 1 provides technical specifications for
radiators and convectors which are permanently installed in a building and fed with hot water or steam below 120°C from a remote heat source. Part 2 specifies the laboratory apparatus, test method and criteria for selecting test samples. It also
characteristic equations to be determined for different sizes or models of the same type. Similarly, surface temperatures are measured at various water temperatures and characteristic equations can be derived to predict surface temperatures at different operating conditions.
LST natural convectors
The table above shows performance data for a typical Low Surface Temperature (LST) natural convector, which is wall mounted with a casing width of 1,500mm. The casing includes an outlet grille on the casing top and inlet grille on the bottom of the casing, with a hot water emitter connected to LPHW flow and return. Air temperature is taken at 0.75m above finished floor level. A review of the results can yield the following conclusions: i) Greater output is achieved from the stack effect. An increase in the height of the casing will induce better airflow and heat transfer, leading to higher thermal output. ii) This leads to a reduction in maximum surface temperatures at the outlet grille on top of the casing. iii) Reducing the return temperature will only lead to a lower mean water temperature. This reduces output, but will not reduce grille surface temperature, which is determined by the water flow temperature. iv) Reducing the water flow temperature will reduce output as well as bringing the grille surface temperature down to an acceptable value when selected in conjunction with an appropriate casing height. v) A reduced room design temperature will increase heat output by virtue of a greater mean temperature difference across the emitter and also lead to reduced grille surface temperatures.
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