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BUILD 115 December 2009/January 2010 57 SUSTAINABILITY PLAN YOUR HEATING The best heating system for a particular home will always depend on many factors, from location to lifestyle, but it’s best to plan for it at the start of the design process. By Albrecht Stoecklein, Sales Manager – Specifiers, Right House, Wellington H eating is often an afterthought in New Zealand house design, and the consequences of this are clear. The BRANZ HEEP project and other research by the University of Otago Energy Studies Programme and the Wellington School of Medicine and Health Studies has consistently shown that we are paying for this ad-hoc approach with cold and damp houses, high power bills and serious health effects, primarily for children and the elderly. From fireplaces to heat pumps Heating hasn’t always been left out of house designs. Until the 1950s, most New Zealand homes had inbuilt fireplaces. Then, from the 1960s onwards, heating was no longer incorpor- ated in the design, often to save costs and because cheap, convenient plug-in electric heaters were readily available. The recent rapid growth of split air-to-air heat pumps is changing this. Integrated heating solutions Parallel to this has been another slow but steady increase in more integrated systems. The two main technology types are ducted or multi- split heat pumps and, more recently, hydronic underfloor and in-slab heating systems. Whether driven by consumer demand or as a ‘value-added’ feature promoted by builders, underfloor heating has become increasingly common in high-end house designs. Often, the basic underfloor system is enhanced with hydronic radiators in the upstairs bedrooms and/or by integrating domestic hot water. In-slab heating needs programming In-slab heating pipes are laid in individual zones. Due to solar access, different parts of the floor receive sunlight during different times of the day. Therefore, careful consideration of both the piping layout and the location and type of thermostat and controller is required. Programmable controllers are a ‘must’ because of the slow response time of underfloor heating systems. Unlike an air-to-air heat pump, which can increase the room temperature within 15 minutes, the underfloor system must be programmed due to its less rapid response. Air sensors may provide more accurate feedback to controllers and pumps than in-slab sensors, particularly if the floor will receive widely varying sunlight. Air sensors have a drawback in that they react quickly to short temperature fluctuations caused by draughts or clouds. This may cause the controller to switch the hot water pipe flow on and off more rapidly than is necessary for an underfloor system. Which heat source? One of the big decisions is the heat source. Historically, the only viable options were gas or, less commonly, diesel or solid fuel boilers. These have the advantage of high energy densities and therefore high power outputs, placing few limitations on system integration (underfloor, radiators and domestic hot water). The main concerns are usually the availability of gas on site and future gas prices, which are less predictable than electricity prices. An alternative heat source type has recently become more common. Air-to-water heat pumps with split compressor units and cylinders can supply the hot water for space heating and domestic water heating. Having a coefficient performance of three means that running costs can sometimes be lower than for gas or diesel. Unlike gas and diesel boilers, heat pumps have a limited power density and lower maximum temperature (50–60°C). An underfloor heating installation. The Right House demo hut with a cut-away section of the underfloor heating and wall and ceiling showing double layers of insulation.
