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Home , Underfloor heating

Plan your heating The best 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

eating is often an afterthought in New Zealand house design, and the consequences of this are clear. H 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 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 An underfloor heating installation. 1960s onwards, heating was no longer incorpor­­ ated in the design, often to save costs and because heating systems. Unlike an air-to-air , cheap, convenient plug-in electric heaters were which can increase the readily available. The recent rapid growth of split within 15 minutes, the underfloor system must air-to-air heat pumps is changing this. be programmed due to its less rapid response. Air sensors may provide more accurate Integrated heating solutions feedback to controllers and pumps than in-slab Parallel to this has been another slow but steady sensors, particularly if the will receive increase in more integrated systems. The two widely varying sunlight. Air sensors have a main technology types are ducted or multi- drawback in that they react quickly to short split heat pumps and, more recently, hydronic temperature fluctuations caused by draughts or underfloor and in-slab heating systems. clouds. This may cause the controller to switch Whether driven by consumer demand or as the hot water pipe flow on and off more rapidly a ‘value-added’ feature promoted by builders, than is necessary for an underfloor system. underfloor heating has become increasingly common in high-end house designs. Often, Which heat source? the basic underfloor system is enhanced with One of the big decisions is the heat source. hydronic radiators in the upstairs bedrooms Historically, the only viable options were gas and/or by integrating domestic hot water. or, less commonly, diesel or solid fuel . These have the advantage of high energy The Right House demo hut with a cut-away section of the In-slab heating needs programming densities and therefore high power outputs, underfloor heating and wall and ceiling showing double layers of insulation. In-slab heating pipes are laid in individual placing few limitations on system integration zones. Due to solar access, different parts of (underfloor, radiators and domestic hot water). supply the hot water for space heating and the floor receive sunlight during different times The main concerns are usually the availability of domestic water heating. Having a coefficient of the day. Therefore, careful consideration of gas on site and future gas prices, which are less performance of three means that running costs both the piping layout and the location and type predictable than prices. can sometimes be lower than for gas or diesel. of and controller is required. An alternative heat source type has recently Unlike gas and diesel boilers, heat Programmable controllers are a ‘must’ become more common. Air-to-water heat pumps pumps have a limited power density and because of the slow response time of underfloor with split units and cylinders can lower maximum temperature (50–60°C).

BUILD 115 December 2009/January 2010 57 The system design can therefore become more electronically complex, and a small amount of booster heating controlled actuators auto air bleeder may be required to meet the weekly 60°C water temperature required by the Building Code. temperature gauge electronic control board isolation valve Radiators may need to be sized larger than for systems. As more heat pumps capable of flow valves and 4 bar pressure gauge flow meters higher temperatures appear on the market, this limitation may disappear.

manifolds Comparing the sustainability pump New Zealand-specific CO2 emissions are about 0.6 kg/kWh for electricity, whereas emissions from gas burnt on site are only isolation valve 0.2 kg/kWh. Taking account of the heat pump efficiency of 300%, both options are therefore Typical control panel for underfloor heating. quite comparable. A similarly balanced argument applies for fuel costs at about 8c/ warm floor under your feet, no draughts and no factors such as climate, budget, house size, fuel kWh for gas and 25c/kWh for electricity. ugly radiators or heat pump units on the wall. availability and the lifestyle of the homeowner. Combine this with a well designed house The key to getting the best outcome is Underfloor heating expensive making use of free solar gains and superior teamwork between the heating system specifier, Irrespective of the heating source, insulation and windows, and integrated heating the designer and the client during the concept systems with large underfloor components are solutions add real ‘comfort value’ to a home. design stage. inherently more expensive to run than air-to-air For more information on Right House design heat pumps and possibly even small individual No silver bullet, just good planning advice and energy products and systems, visit radiators – if these are used carefully. However, There is no silver bullet. The best heating www.righthouse.co.nz. central heating has its attractions, including a system for a particular home depends on many

58 BUILD 115 December 2009/January 2010