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Green Smart Magazine : 2009_new
greensmart 9 73 If mechanical heating is required, energy-efficient heaters or those powered by renewable energy should be used. Two different methods of heat delivery are hydronic heating and heat recovery/heat shifting. Hydronic heating is a mix of radiant and convective heat which can be designed to efficiently heat the home to the desired temperature. Hydronic heating operates by recirculating hot water in wall-mounted panels throughout the house, while in-slab floor heating is pipework that is embedded in a concrete slab. The water can be preheated by solar, geothermal heat pump, natural gas or electricity, and the pipework can be integrated with other household hot water to help reduce energy consumption. The greatest energy savings (and consequent reduction in carbon emissions) come from preheating the water using solar first, then geothermal heat pump or gas. Using traditionally-sourced electricity for this purpose is the least desirable option. There is a range of benefits with hydronic heating: • it is silent • it can be isolated to where the heat is needed • temperatures can be individually controlled for different room needs • radiant wall panels can be safe to touch when temperatures are set appropriately. Radiant wall panels and in-slab heating are best installed during construction stage. Note that hydronic heating will not deliver instantaneous heat as the water circulated in the pipework will need to be preheated. In-slab pipework will also need to heat up the slab that it is in contact with. However, a timer can be used to optimise heating requirements. Heat recovery, active solar collectors (also known as solar thermal or solar air heaters) and heat shifter systems are designed to capture heat in an area and move it to desired locations within the house through the use of a low watt fan and ducting. Heat recovery and heat shifter systems can be placed in the roof cavity or within the wall structures and can be fitted with a temperature gauge to control the heat moved. Active solar collectors use a panel mounted either on the roof or wall of a building to harvest solar radiation into heat or cool energy which is then ducted into the building using a fan. Even during winter, solar radiation heats the air in the roof space or solar collector and this heat can be used to dramatically reduce artificial heating requirements. It is important to note that as we seal homes tighter to maintain the thermal envelope of the house (especially during winter), indoor air quality can be compromised. Heat recovery ventilators, solar collectors and heat shifters provide fresh air and often use filters to purify the air and also significantly reduce energy usage for heating and cooling. In multi-storey homes uncontrolled movement of heat can mean cold temperatures on the ground floor and hot temperatures in the floors above. Heat benefits of a geothermal cooling system > Photo courtesy HRV Photo courtesy Hills Solar ACTIVE SOLAR COLLECTORS USE A PANEL MOUNTED EITHER ON THE ROOF OR WALL OF A BUILDING TO HARVEST SOLAR RADIATION INTO HEAT OR COOL ENERGY • quieter operation than conventional airconditioning • low running costs because of the Earth's free heat sink • free hot water heating by extraction of heat from the house • reverse cycle for heating and cooling modes at no extra cost • adaptable to any inside cooling configuration.