Delivering Part L to apartments

The key to bringing the energy-efficiency benefits of central plant and renewable energy to individual dwellings in a multi-apartment block is an interface based on a plate heat exchanger — such as the Danfoss Redan range from Taconova.
Multi-apartment buildings and multi-storey flats need a centralised approach to energy-efficient plant and exploiting renewable energy, while still permitting individual control and metering for each dwelling. JOHN COOPER explains how this could be achieved.Revisions to Parts F and L (ventilation and fuel conservation, respectively) of the Building Regulations, scheduled to come into force from April 2006 as part of the Government’s implementation of the Energy Performance of Buildings Directive (EPBD), are designed to make a major contribution to the UK’s commitment to combat climate change. Reducing carbon emissions and achieving greater efficiency from all specified systems should be firmly at the forefront of the agenda of every building-services professional. Popular Multi-dwelling development continues to prove popular, with home builders finding a ready market for their properties, especially amongst the new breed of city-centre urbanites. With energy-efficiency obligations in mind and the need, in some cases, to use a percentage of renewable energy to obtain planning permission, the modern apartment project presents a particular set of challenges to the building-services design team. Whether it be a brand new scheme, a conversion or if it forms part of a mixed-use development, the above criteria will affect the type of heating and hot-water installation fitted along with other key factors. These include minimising up-front construction investment costs, providing a reliable supply, maximising the use of space in the building for its actual purpose, and, of course, satisfying the heating and hot-water needs of the eventual apartment owners. Central plant One option that merits due consideration more than ever is the central supply to each apartment from a central boiler plant, CHP or district-heating substation. These heat sources work in combination with decentralised units (also known as interface units) in each apartment to control the heating and supply of domestic hot water. Such units normally incorporate a compact plate heat exchanger, which delivers instantaneous water heating on demand, and a differential-pressure control valve to control the heating flow to the occupants’ radiators, typified by the Danfoss Redan range, now available in the UK from Taconova. An optional built-in energy meter and water meter allows energy and water consumption to be monitored and, if necessary, billed.   In applications where the central heating plant has an oil- or gas-fired boiler, the primary flow temperatures can be adjusted according to the ambient temperature, ensuring high energy efficiency. Typically, a winter flow temperature of 80°C for the heating system can be reduced to 60°C in summer when heating is not required. The concept of a decentralised unit in each apartment also opens up the opportunity of using combined-heat-and-power (CHP) plant, with its well known efficiencies of heat and power generation. Main criteria There are two main criteria in selecting the correct type of decentralised unit. First, is the system indirect or direct heating? In a direct heating system, when the flow from the main plant feeds an individual apartment’s radiators, the flow rate is normally controlled by the use of a differential-pressure control valve set to optimise the flow rate through the local heating circuit. Indirect heating systems, where a separate plate heat exchanger is used to separate each apartment’s heating system from the main plant, are normally used in high-rise developments. In these cases, the system pressures are high or the pressure limits of existing radiators and pipe work are unknown. The other key factor is tap load. A 35 kW unit gives a nominal tap flow rate of 12.5 l/min, which is usually perfectly adequate; a typical combi boiler delivers less flow. Larger units can deliver a flow rate up to 19 l/min. Controlling lime-scale is an important advantage of this concept. A pressure/temperature (PTC) control valve to regulate the flow of primary heating water based on domestic hot water demand is the most effective type of control. Lime-scale build up is eliminated because ‘hot’ primary water only passes into the plate heat exchanger when a demand is generated by opening a tap (the valve senses the fall in pressure), thus minimising the water temperature in the heat exchanger. Energy efficiency Increased energy efficiency is possible through improved boiler or district-heating installation operation. Heat loss in the distribution network is significantly reduced compared with conventional central plant solutions, since a circulation line for hot water and domestic water is not required. At the same time, individual adjustment of room temperature and independent DHW production is possible, achieving greater energy efficiency. The system also ensures that accurate energy bills can be easily created for each apartment, by enabling remote reading with an accurate energy meter. Space-saving benefits are also impressive. Only three ascending pipes are required in any building (cold water and heating supply and return). The Redan unit in each flat requires only a small amount of space and eliminates the need for individual DHW cylinders. Additional positives are the inherent health, safety and maintenance advantages. They include a bacteria-free method of producing DHW production, which will minimise the risk of Legionella. Safety is also enhanced because gas is not needed for heating and DHW in each flat. Meanwhile, the simple operation of each unit minimises maintenance in each flat. Proven This approach to heating and DHW is proven in numerous installations across Continental Europe and is more energy, cost and space efficient than solutions based on electric or gas boilers and DHW cylinders. John Cooper is managing director of Taconova UK Ltd, 20 New Forest Enterprise Centre, Totton, Hants SO40 9LA.
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