Compliance of Standard Low Cost Provincial Government Houses 2014/05/05

Transcription

1 SANS XA Compliance of Standard Low Cost Provincial Government Houses Deemed to Satisfy Route 2014/05/05

2 Introduction The following items will be covered in the presentation Introduction to SANS XA. The compliance of two standard low cost Provincial Government house (Type H3) are to be assessed according to the deemed to satisfy route of SANS 10400XA. Estimated Energy Uses of the low cost houses to be illustrated

3 SANS XA options to demonstrate compliance There are 2 routes (options) available to demonstrate compliance: Deemed to satisfy (prescriptive route) This route requires that all external walls, roofs, floors with under-floor heating and fenestration (windows) adhere to minimum thermal requirements. A minimum R-value (thermal resistance value) is specified for external walls, floors and roofs while for fenestration a calculation is specified in SANS 204. Rational Design When using the rational design route there are no stipulated requirements for specific R-values or restrictions to the type & amount of glazing used on the building and also mechanical services as there are in the deemed to satisfy route. The rational design route requires certified building simulation software to be used to calculate the energy use and maximum power demand of the building. There are 2 options to demonstrate compliance via the rational design route: Stipulated values route Reference building route

4 Schematic Representation of SANS 10400XA Compliance Routes

5 Mandatory requirement for hot water production Both of the deemed to satisfy and rational design routes need to comply with the hot water requirements which are as follows: A minimum of 50% by volume of the annual average hot water heating requirements shall be provided by means other than electrical resistance heating. The alternative means could be via but not limited to heat pumps, solar water heating, heat recovery from other processes or heating via gas. Hot water installations need to comply with further SANS requirements as provided in section 4.1 of SANS10400XA

6 Climatic Zones defined for SANS XA calculations

7 General SANS 10400XA Guidelines Orientation: The building should be compact in plan, with the rooms that are used most and the major areas of glazing placed on the northern side of the building to allow solar heat to penetrate the glazing during the winter months. The building orientation requirements are generally taken as a guideline rather than a requirement. Fenestration calculations as per SANS 204 automatically restrict the amount of fenestration for each orientation for the deemed to satisfy route.

8 Deemed to satisfy route External Walls Non-masonry walls shall achieve a minimum R-value* of a) climate zones 1 and 6 : 2,2 m² K/W b) climate zones 2,3,4 and 5 : 1,9 m² K/W The following types of masonry walling comply with the R-value requirements: a) double-skin masonry with no cavity, plastered internally, or rendered externally; or b) single-leaf masonry walls with a nominal wall thickness greater than or equal to 140 mm (excluding plastering and rendering), plastered internally and rendered externally. NOTE Minimum R-value of masonry walls : 0,35 m² K/W *R-value provides an indication of the resistance to heat flow e.g. the higher the R-value the better the insulating properties of the wall

9 Deemed to satisfy route Roof assemblies A roof assembly shall achieve the minimum total R-value specified in table 7 for the direction of heat flow according to climate zone. A roof assembly that has metal sheet roofing fixed to metal purlins, metal rafters or metal battens shall have a thermal break consisting of a material with an R- value of not less than 0,2 m² K/W installed between the metal sheet roofing and its supporting member.

10 Deemed to satisfy route Fenestration Buildings with up to 15 % fenestration area to nett floor area per storey comply with the minimum energy performance requirements. Buildings with a fenestration area to nett floor area per storey that exceeds 15% shall comply with the requirements for fenestration in accordance with SANS 204. The SANS 204 specifications on fenestration has two options: Mechanically ventilated buildings Naturally ventilated buildings (Generally used for residential buildings)

11 SANS 204 requirements for glazing Naturally ventilated SANS 204 provides a methodology for calculating the maximum allowable percentage glazing as a percentage of the façade area for each orientation. These calculations restrict the percentage glazing allowed for each orientation dependant on: The SHGC (Solar Heat Gain Coefficient) and U-value of the glass Whether there is shading provided The climate zone

12 SANS 204 glazing example Naturally ventilated The table below provides an indication of the maximum allowable glazing for each orientation for 2 types of glazing for Cape Town, climate zone 4 calculated as specified in SANS 204 SANS Naturally ventilated building Glazing Percentage (valid for climate zone 4) Allowable Glazing as Percentage of Façade Area Single clear glass (U=5.6; SHGC=0.77) Double clear glass (U=3.0; SHGC=0.68) Double clear glass with shading (U=3.0; SHGC=0.68) NORTH NORTH EAST EAST SOUTH EAST SOUTH SOUTH WEST WEST NORTH WEST From the table above we can deduce the following: As the insulating properties (i.e. U-value decreases) of the glass improves the % glazing allowed on the southern facades increases. If the building is well shaded then the allowable glazing on all facades increases If the shading coefficient i (SHGC) of the glass decreases then the glazing allowed on the northern facades increases

13 Rational design route - Stipulated values route The calculated annual energy as determined via building simulation and further manual calculations for lifts and hot water etc. need to be less than values specified in tables 2 & 3 of SANS XA as indicated below: Note that there are a limited number of building classifications for this particular route while building classifications not listed in these tables would need to pursue the reference buildings route

14 Rational design route - Reference Building Route This method requires a model of a reference building to be built and simulated as well The energy consumption for the actual building is then required to be less than that of the reference building The reference building has the same geometry as the actual building but its envelope and services need to comply with the deemed to satisfy requirements The preferred route would be to comply via the stipulated values and only if compliance is not possible via stipulated values a reference building would need to be built

15 Assessment of houses - fabric The table below compares the fabric of the 2 houses to the requirements of SANS XA: External Walls Fenestration Min SANS 10400XA 40m² House Compliant 43m² House Compliant Requirements min 140mm wide, masonry walls with min min 140mm wide masonry, min Type masonry min 12mm Yes Yes total R value of mm plastered outside only plastered outside only Min R value of total 0.35m² K/W 0.37 Yes 0.37 Yes construction Ground Floor Fenestration area up to % Yes 6.56% Yes % to nett floor area per First Floor storey NA 8.28% Yes Roof Min R value Total Roof Assembly (m 2 K/W) No 1.74 No All other fabric is compliant except for the roof assemblies of the 2 houses which would require the following in order to comply: the 40m 2 house currently has 50mm glass wool which would need to be increased to a minimum of 140mm the 43m 2 currently has 40mm Isoboard which would need to be increased to a minimum of 100mm NOTE: Masonry walling can be referring to a wide range of materials used in construction such as brick or various other stones such as granite marble, cast stone, concrete block etc. however for the purposes of this study it will be assumed that masonry refers to commonly available concrete brick with conductivity of 0.61 W/mK

16 Assessment of houses hot water requirements None of the 2 houses have alternative hot water heating systems specified and it is therefore assumed they currently have conventional geysers. In order to comply they would require a heat pump or solar water heating system sized to supply a minimum of 50% of the water heating requirements. Natural gas is also an option if available.

17 Conclusion Both designs can be rendered compliant by amending the roof insulation appropriately the 40m 2 house currently has 50mm glass wool which would need to be increased to a minimum of 140mm the 43m 2 currently has 40mm Isoboard which would need to be increased to a minimum of 100mm Hot water generation to be at least 50% by non electric resistance heating Solar water heating Heat pump Gas

18 Estimated Energy Low cost houses are unlikely to have an air-conditioning system and the only fixed services would be the lighting, geyser and stove. The rest of the energy use would come from plug loads of the appliances The energy use of a typical house and its appliances has been provided in the table below assuming the house uses an electric stove and a conventional geyser Appliance Power use (watts) Ave hrs/day in use 40m² House 43m² House Energy Consumption Energy Consumption Number of Rooms per year (kw/year) Number of Rooms per year (kw/year) Television Cell Phone Charger Kettle Electric Stove Microwave oven Geyser (Electric) Fridge with freezer Iron Lighting CFL(12W) It can be noted from the above table that the larger energy uses are from the electric geyser and electric stove