Adelaide Homes Design Guide 4 - Winter warming

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1 Adelaide Homes Design Guide 4 - Winter warming Adelaide's temperate climate means home warming is required during winter. There are many efficient heating systems. The most economical method, however, is to use the sun's own radiation. Introduction The first and most important principle of efficient winter warming is to prevent heat from leaking out of the house once it has been generated. The full list of winter warming principles we'll cover in this leaflet are: 1. Keeping heat inside 2. Using the sun's radiation 3. Creating heat inside 4. Storing heat within a building's envelope Conduction doesn't happen very efficiently through a gas because the molecules that make up its bulk are much further apart than in a solid or a liquid, so they don't come into contact with each other and transfer their heat from one side to another as readily. This makes gases (such as air) good insulators, as long as they can be trapped in place. This is why winter jackets are puffy; the trapped air in the lining acts as a barrier between your body heat and the outside environment. The interior of an insulated wall warms up just as a non-insulated wall would, but this heat cannot easily pass through the layer of insulation material. The interior of the room therefore will not lose heat to the external environment and will remain warm, while the exterior surface of the wall will remain cool. The temperature difference is preserved. 1. Keeping the Heat Inside Heat is transferred by radiation or conduction. Radiation is the process of releasing heat to the open surroundings, while conduction is a process of heat moving through the bulk of a solid or liquid material from one side to another. Heat penetration through wall from sun the wall heat radiation Home insulation works in much the same way, preventing heat from moving completely through the bulk of a wall. 1 suns radiation absorption surface heat conduction

2 If air is allowed to leak through the building envelope into the insulation material, it will gradually push out the air trapped inside it. This continuous replacement means that cold, fresh air meets the wall, and carries away some of its heat. -5 C +10 C 22 C -5 C 22 C Heat penetration through insulated vs non-insulated wall This means that properly installed insulation, good airtightness and well-sealed airlocks are important home elements that keep warmth inside. Insulation The greatest individual loss of heat from any element of the home is through the top, so the most insulation should be placed between the ceiling and roof. Without insulation, around 25-35% of heat is lost via this route. Insulating the roof space above the ceiling increases the temperature difference between the environments each side (the outside air above and the inside room air below). Around 10-20% of heat is lost through the floors. It is important to insulate the edges of ground slabs and suspended timber floors. One popular method to reduce floor heat loss is to carry out construction on a waffle pod slab. Approximately 15-25% of heat is lost through the walls. Though insulation level is often limited by frame width, 2 sufficient insulation must still be achieved. Even high mass walls (such as double brick or rammed earth) need some level of insulation. Glazing The weakest points in your home's insulation are glazed surfaces. When sizing windows, there must be a balance between maximizing daytime heat gain and minimizing nighttime loss. In winter, there are only five hours of solar heat gain in each day. The other nineteen represent a period of heat loss. An appropriate U value (value of conductivity) and SHGC (solar heat gain coefficient) are required to maintain good heat balance. Glazing also has a significant impact on your home's energy rating. Earth Besides building structural insulation, the home can be protected even further from cooling by placing deposits of earth around the façade, or by covering the roof with a layer of soil with cultivated vegetation. Earth deposits are also good protection from cold winter winds. Earth is a very good insulator, maintaining a reasonably constant temperature all year round. At a depth of 0.5m, variations are less than 10C between summer and winter, and are very small across a period of a day. roof soil room insulated by earth earth

3 The average winter temperature at this depth is 15 C, which means that earth-sheltered or underground homes need to overcome an interior / exterior difference of only 5 to 7 C in winter, in contrast to the 20 to 30 C difference that above-ground homes face. Airtightness Heat leaks through junctions between building elements, especially doors, windows and vents. Air leakage adds almost 15-25% to winter heat losses from a building. In addition to proper insulation, all junctions must therefore be well-sealed. One of the best ways to achieve an airtight building is by combining XPS foam cladding with double-glazed upvc windows. Airlocks Opened doors can cool a space quickly, so the best solution is to have an airlock: an entry separated from the heated space by another door. During a clear summer day, the amount of solar energy that falls on a horizontal surface is approximately 1kW/m2 The efficiency of active solar collectors depends upon the intensity of direct solar radiation landing on the panels, whereas passive heating methods also depend upon the amount of material used to capture the heat (the thermal mass) and the air-tightness of the system. Trombe wall These walls are built as part of the north façade from concrete, brick or stone immediately behind a large panel of glass. As they face north, they are exposed to the sun. They use the thermo-siphon effect to heat the interior room space behind. hot air glass pane cold air entrance through an air-lock Trombe wall mass wall air movement with an airlock 2. The Sun's Radiation The use of the sun's radiation for heating your home can be passive or active. In the passive house, heating is obtained by using architectural elements (north-facing windows and sunrooms) to take advantage of physical laws, while the active house uses external technical elements like roof-mounted solar collectors. 3 As the air between the glass pane and the dark surface heats and rises, it exits through an opening in the top and enters the room behind the wall. Meanwhile, the cooler air in the room sinks down and enters the space of Trombe wall through openings at the bottom. The mass of the wall is the heating element itself. It accumulates heat, radiates it into the airspace, and the air then carries the heat into the room.

4 Properties of glass Glass has the ability to let through visible light, a small part of the UV spectrum, and a large part of short-wavelength infrared radiation, but it cannot let through long-wavelength infrared radiation. This combination allows the greenhouse effect to take place, as long-wavelength infrared radiation is felt as heat. Some of the solar rays that pass through glass panes are absorbed by building materials and furniture, and are then re-released as longer-wavelength infrared rays which stay trapped inside, warming the interior. visible light short wavelength long wavelength A sunroom should have massive wall located in the place of the most direct sun radiation, and be painted in dark colors for greater absorption. Behind the wall should be spaces that are used daily. To be efficient, a sunroom must have a north/northwest orientation. During the day, the whole sunroom becomes hot and that warmth is transmitted into the house and into thermal storage systems. The heat is distributed by convection (air movement) through wide doors, sometimes requiring additional mechanical ventilation. sunroom glass surface light penetration through glass air circulation in sunroom Sunroom (conservatory) The sunroom, as an architectural element, has its tradition. It is a connection between external and internal space, it acts as visual and thermal transition zone, and it makes the façade appear richer. Thermally, it benefits from a mixture of direct incidence and a Trombe wall effect. As the sun's rays are trapped by a glass surface, the air in the sunroom heats up and is then distributed through the doors to the heated spaces in the home. The optimal surface area of a sunroom must be calculated individually for each home, but usually there should be 0.5-1m2 of floor space for every 1m2 to be heated in the rest of the home. The area occupied by construction elements should not exceed 10% of that given to glazed surfaces. Passive house All of the physical laws that allow passive elements to heat a space can work in reverse. Glass cannot keep heat inside when the outside temperatures fall. 4

5 Sunrooms must have proper thermal shading of glass surfaces, and doors must be sealed during the night. The openings in a Trombe wall must be closed during the night to avoid cooling of the air in the home, and shading inside to prevent overheating during the summer. This means that a truly passive house requires that you, as the occupant, do some work to position these different heating, cooling and ventilation elements for best effect. You can also use home automation to achieve the same outcome, but with greater expense. Active solar elements Various sorts of solar collectors can be applied to north-facing roof slopes. Thermal collectors are warmed by the heat of the sun. Heat is then transported over heat transfer fluid (water, air or antifreeze) and used for warming the water or warming the home. As the flat collectors can use only direct sunlight, they are not a very reliable heat source and so solar collectors should be used for warming the home only when other more efficient systems are not available. Solar photovoltaic collectors transform light energy into electric power. These can be coupled with battery systems to completely remove the need for your home to be connected to the grid. 3. Creating Heat Weather conditions greatly influence the amount of available sunlight. Over the course of a few successive cloudy days, or in winter, passive home heating elements will not produce sufficient warmth. The home must therefore also be equipped with one or more additional heating systems. Heat banks A heat bank is an electrical storage heater. It uses electric power during the night, when the base load electricity is available at lower cost, to heat a thermal mass inside (clay brick or ceramic). It releases this stored heat during the day when it is needed. storage heater solar panels on roof 5 The stored heat is radiated continuously, but the heat transfer can be sped up by mechanical fans that move air through the heater. Heat banks usually have two controls - one that controls the amount of heat stored, and another that controls the rate at which the heat will be released.

6 These controls may be operated by the user or by thermostat set to a desired temperature. Heaters using other fuels are usually switched off during the night, meaning you wake up to a home that is cold in the morning. As heat banks work during the night, the home remains warm both in the night and in the morning. The down side of heat banks is that they are a stored heat system, meaning they will release their heat during the day regardless of outside temperatures. Also, if it suddenly gets cold or you forget to turn them on the night before, the heat banks will have no heat to radiate the following day. Additional heaters should not be placed under windows or on the external walls at all, as they will increase the heat flow from inside to outside. Heaters should be ideally placed near thermal masses such as internal brick walls or other masonry items. floor with inlaid pipes Advantages: Heat is evenly distributed in the room, so there are no warm and cold spots dependent on air movement. Minimal movement of allergens. Floors are warm under foot. One system can be used for both heating the space and preparation of hot water for showering. Fireplace A fireplace is a beautiful architectural element used to create a relaxing ambiance and, with proper design, it can be used for heating the room. Hydronic heating Hydronic heating is a system of tubes which circulate hot water. These tubes can feed radiators, or can be laid down into the concrete slab of your home. Gas or electric boilers heat up the water which is then pumped through the tubes. Most systems are best coupled with an electric heat pump fed by roof-mounted solar panels. fireplace 6

7 Modern fireplaces use a fire back - a cast-iron or steel plate placed behind the fire - to reflect the heat into the room. Glass doors also increase the efficiency of your fire place. They work by trapping the hot air inside the fire for re-burning and allowing more heat to radiate out, increasing the efficiency of the fireplace overall. Masonry heaters are the most efficient type of fireplace. They transport the fire's exhaust through channels in order to heat the brickwork. After around 2 to 4 hours of burning, the bricks absorb enough heat that they are then able to radiate warmth for the next 12 to 24 hours. This makes this type of fireplace a powerful radiant heater, although it cannot produce heat immediately - only after several hours. Air conditioning (AC) This is the least energy-efficient system for heating and cooling. Air conditioning is a process of improving thermal comfort and air quality, specifically humidity, in occupied indoor spaces. Although AC usually means cooling your home, reverse-cycle air conditioners can heat the space as well. They absorb heat from the outdoor air and give it to the indoor air. Conditioning the air is a very important issue when you have built an airtight home. Ventilation through an open window can greatly reduce the inside temperature during cold winter days. Ventilating systems that can recuperate heat from the waste air will significantly improve energy efficiency. The old, warm air is distributed outside but its warmth is used to heat the incoming air. Air conditioners have a certain noise level. The outer unit should be far removed from quiet spaces. Heat pump This is a thermodynamic machine similar to an air conditioner, but it works in the opposite direction. A liquid with a boiling point of -5 C evaporates inside the pipes of the heat pump when those pipes come into contact with atmospheric air outside the home (as the air is warmer than -5 C). In the process of evaporation, heat is taken from the air and is used to boil water in a water tank. The evaporated liquid, now a gas, is then transferred further to the compressor to be condensed into a liquid so that the process can begin again. Heat pumps do use a lot of energy; however, coupled with a 5kW or greater solar array, they are one of the most efficient methods of heating water for domestic use and for underfloor heating. 4. Heat Storage Thermal mass is used to store heat from the sun and re-release it with a delay during colder evenings, night, or the next sunless days. The main characteristic of a thermal mass storage system is thermal lag - the amount of time needed to material to absorb and then radiate the heat, or the time needed for heat to be conducted through the specific depth of material. 7

8 heater suns radiation Stone is used as thermal storage mostly under the house. It typically consists of 3-10cm rocks and it is estimated that one house needs around 6-15 tons of rocks for sufficient heat storage. Water has a greater capacity for storing heat, and one house needs around 6000 l of water (nearly 1m2 of collectors is required for l water). Thermal lag is influenced by: the density and conductivity of a material; the difference between temperatures on each side; the thickness of the elements; and exposure to air movement. During a clear summer day, when the sun is highest in the sky, the energy that falls on a horizontal surface of one m2 is 1kWh. If we could use this energy for warming 10 l of water, the temperature will rise from 10 to 96 C in one hour. The thermal mass should be located where it will be exposed to direct solar radiation or heated by a radiant heat source. Calculating the mass required in any given home is a important. A rough guide for the design of any room where a thermal mass will be placed in the temperate climate of Adelaide is that the ratio of glass-to-floor-area should be 12-15% (17% for double-glazing). Avoid using thermal mass on upper floors. The temperatures of these floors are higher due to the rising of hot air, so the thermal mass will absorb this energy, cooling the home. Ideal elements for thermal mass are suspended concrete slabs (not earth-coupled), masonry walls, water containers, and phase change materials (such as BioPCM). 8 water columns Phase-change materials (PCMs) are lightweight substitutes for thermal mass, and have a greater ability to store heat. A material which melts in high temperatures (25-35 C) stores heat and releases it while it cools down again and re-solidifies. PCMs and water-filled tanks are much lighter than masonry and need no additional support on upper floors, yet they have a greater heat storage capacity. Another benefit is their mobility; they can be moved outside during summer time, or drained altogether (in the case of water tanks). They can be positioned in direct sunlight and then moved to rooms that require additional heating. CALL NOW TO DISCUSS YOUR NEW HOME: Architectural Energy Efficient Homes