Solar Home Design and Thermal Mass

Transcription

1 Solar Home Design and Thermal Mass Solar Home Design And Simulation of Thermal Mass Stefan Fortuin

2 Papers Renewable Energy System Design Renenwable En Conversion Devices Energy Policy Greenhouse Science and Policy Source:

3 Five Solar Thermal Principles See document design for the sun!! 1. Heat Gain Heat gain refers to the heat accumulated from the sun: Solar-thermal-heat is trapped using the greenhouse effect. The ability of a glazing surface to transmit short wave radiation and reflect long wave radiation is known as the greenhouse effect. 2. Heat Transfer Heat is transferred by conduction or convection. Convection: hot portions of a liquid or gas will rise and cold portions above it will sink. Conduction rate of heat transfer has to do with the conductivity of the medium and the temperature differences. 3. Heat Storage Heat transfer to a storage medium can be maximized with the aid of a multi tank heat storage vault system. 4. Heat Transport Heat transport from solar collector to heat storage vault. In cold climates it is important to separate the heat collection area from heat storage area. Closed loop systems use a circulator pumps to transport heat from sun to storage vault. Warm climates use simple batch heaters, water tanks enclosed inside glazed boxes. 5. Heat Insulation A solar home is worthless without adequate insulation: About R25 in the walls and R35 in the roof/ceiling area. Heat storage vaults and heat transport tubing should also be well insulated. Sunrooms must be isolated from living quarters with doors or drape to prevent heat loss at night. Source:

4 Energy End-use in NZ Houses Source: BRANZ 1998, Conf. paper NO.57

5 Energy End-use in NZ Houses Source: BRANZ 1998, Conf. paper NO.59

6 Energy-wise Renewables 11 Passive Solar Design for NZ Homes: Since solar energy is free, why aren t many more homes in New Zealand designed to use passive solar principles to provide space [or water] heating? Source: EECA

7 Seasonal Sun Path Source: EECA: Energy-wise Renewables 11: Passive Solar Design for New Zealand

8 Solar Room Orientation Source: EECA: Energy-wise Renewables 11: Passive Solar Design for New Zealand. Adapted from David Pearson s The New Natural House Book.

9 Parameters Reflection (%) Thermal Mass Thermal Conductance (K-Value) Source: EECA/Waitakere CC: Design for the Sun

10 Solar Heat Gain Radiation Conduction Convection Source: EECA/Waitakere CC: Design for the Sun

11 Solar Heat Gain Checklist Ensure that north windows will allow direct sun onto thermal mass for 6 hours on a sunny winter s day, Given the right combination with insulation and thermal mass, the area of northfacing glazing should be about 10-20% of the house s floor area. (You can calculate the area using EECA s Energy Wise Design for the Sun manual to balance the rate of heat loss (dependent on insulation) with thermal mass and local climate) Windows on east or west walls would ideally be 2-5 % of total floor area. On a south wall windows should be the minimum necessary for adequate ventilation and light. Consider the use of clerestorey windows (above the roofline) to bring sun and light into south-facing rooms. For a complex house design, or on a south-facing slope, consider a mix of passive solar systems, using direct, indirect and isolated heat gain where each is appropriate. Eaves or other overhangs prevent overheating by the high summer sun. The average window works well with a mm overhang, while glass doors require mm depending on wall height and orientation. Be very careful with the design of a conservatory. It is likely to overheat in summer unless you build in ventilation and shade, and on winter nights it could leak heat massively if it cannot be sealed off from the rest of the house. The value of a conservatory is in the quality of living space it offers. Ensure that it is also thermally efficient, not a thermal drain. Source: EECA/Waitakere CC: Design for the Sun

12 Solar Heat Gain Checklist In Pictures Source: EECA/Waitakere CC: Design for the Sun

13 Solar Heat Storage Checklist Choose or create site conditions suitable for a solid concrete floor for solar heat storage. The floor offers the best opportunity for thermal and economic performance. A large thermal mass may slow down morning heating up, and too little mass does not store sufficient energy. So choose the correct size of thermal mass. It is possible to calculate your requirement exactly by balancing it with the solar gain and insulation of the house. Alternatively you can use the rules-of thumb that follow. A concrete floor slab should be about 100 mm thick, exposed to direct sunlight, dark in colour,.and insulated underneath. A masonry wall (e.g. brick, concrete, block, etc) should be 100 to 150mm thick, and insulated on the outside. Avoid covering up thermal mass floors with carpet because it reduces the rate of heat absorption. In places where you will be sitting with your feet on the floor you can use rugs for comfort. Avoid air cavities in thermal mass (e.g. fill concrete block cavities). Avoid thermal mass walls in shady areas unless they are well insulated. They will lose too much heat to the outside, without giving the benefit of absorbing the sun s heat. Internal thermal mass walls are better than external as they don t lose heat to the outside at night. However external walls will usually get more sun and offer the most practical solution. A thermal wall of half height will offer some thermal storage while still allowing a view. Make a thermal mass wall into a feature wall. Build it with ornamental stone, artistic earth, patterned bricks, etc. Large Day/Night temperature fluctuations may require active intervention twice a day to maximize passive systems. Source: EECA/Waitakere CC: Design for the Sun

14 Source: EECA/Waitakere CC: Design for the Sun Solar: Active

15 Solar: Active Trombe Wall Thermal Chimney Source:

16 Thermal Mass & Insulation Hot Box Test Envelope configurations: Insulation (I) Thermal Mass (M) Insulation - Thermal Mass (IM) Thermal Mass - Insulation (MI) Th. Mass - Insulation Th. Mass (MIM) Insulation Th. Mass - Insulation (IMI) Insulation Thermal Mass Source: roofs and walls

17 Thermal Mass & Insulation Source: EECA/Waitakere CC: Design for the Sun

18 Thermal Mass & Insulation: Example of Central Thermal Mass Source:

19 Day/Night Influence of Thermal Mass

20 Basics of Building Insulation Vapor barrier Some insulation products absorbing moisture can easily loose up to 50% of its thermal efficiency. Radiation 65% to 80% of all energy that goes from the warm side to the cold side of a wall assembly, summer and winter, is radiant heat. Eflective products, on the other hand, stop approximately 70 % of all radiant heat by reflecting up to 97% of the radiant heat rays. Conduction Stagnant air is a better insulation than any solid material Conventional thermal insulation does not stop heat rays; but rather, will absorb them and transfer heat. Thus, mineral wool and other thermal insulation will only slow down the transfer of heat. Convection/Ventilation Air Changes per Hour (ACH) The number of times one house volume of air leaks through the house in one hour. Test: (de)pressurize a house with ablower to a pressure difference of 50 Pascals and then measure the flow through the blower. Measure the internal air volume of the house and divide.

21 Energy Storage Options

22 Energy Generation Options

23 Advanced Materials Aerogel (foamed glass) Thermal conductivity W/m.K ( % air) (0.024 W/m.K for Air) (0.04 W/m.K for fibre glass/wool) Phase Change Materials (PCM) Hydrides (liquid-solid) Fatty acids and esters (liquid-solid) paraffin (liquid-solid) Used in Wallboard!

24 Phase Change Material

25 Phase Change Wallboard Source:

26 Next: Read: Energy-wise Design for the sun Manual Design a house (architect) Model the House using ALF 3 Determine Renewable Energy supply at the Site Evaluate performance Remodel (iterate)

27 BRANZ ALF 3 ALF 3 Software, Manual, House Insulation Guide Adopted as Compliance Method for NZBC Clause H1 Energy Efficiency Demonstrate the effect of varying: Insulation (loss) Location and Size of Windows (gain) Thermal Storage

28 Source: BRANZ No 51 Annual Loss Factor 3 (ALF)

29 Problems / Limitations Thermal Performance (Utilizable gain) depends on: Requirements of the occupants / design / materials (pre-build) Behaviour of the occupants (post-build) Ventilation, air-tightness Heating schedule intermittent heating favours light weight building, not high thermal mass Available resources / Renewable energy Climate Effective Thermal Mass

30 Source: BRANZ No 51 Effect of Thickness