Passive House Object Documentation

Transcription

1 Passive House Object Documentation Lena Gardens Passive House Project ID 2033 Renovation of a Victorian mid-terrace house in a conservation area in London Project designer: Edward Borgstein greentomatoenergy {HYPERLINK " Fig 1 Front elevation This project was carried out for a private client in Hammersmith, London. The house is a Victorian mid-terrace, built in approximately 1870 with solid brick walls. Due to planning restrictions in the local conservation area, the exterior of the house had to be kept unchanged in appearance. As such, all insulation was applied internally on floors, walls and ceilings, with floor joists rehung to avoid penetration of the insulation. The renovation works were used as an opportunity to redecorate the interior, remedy structural defects in the fabric and extend the house at ground and third floor levels. Special features: - Ground-to-air heat exchanger below existing basement floor - Integrated solar thermal system for hot water, backed up by air-source heat pump - Exhaust-air heat pump inside ventilation system for all space heating - Green roof - Specially designed triple-glazed sash imitation windows for conservation area - Thermal bridges cut off by extensive detailing and rehanging of floors U-value exterior wall 0.10 W/m 2 K U-value party wall 0.27 W/m 2 K U-value roof 0.14 W/m 2 K U-value floor (avg) 0.12 W/m 2 K U-value windows (avg) 0.89 W/m 2 K PHPP primary energy demand 74 kwh/m 2 a Air heat recovery 72% Pressure test n ach PHPP annual heating demand 12 kwh/m 2 a

2 2. Description of construction task The project was undertaken between January and October 2010, with final commissioning and tuning of all systems complete by February Extensive demolition work was carried out in the existing terraced building, removing the roof, the second floor and the plaster from all walls. All chimney breasts were removed and the chimney pots on top of the building were closed off and propped. Where necessary, remedial work was carried out on the existing brickwork and structural steel beams were installed where additional support was required. The kitchen was extended outwards with a side return and the roof was rebuilt as a mansard loft extension; both typical conversions for properties of this age and construction. This increased the usable floor area significantly despite the use of internal insulation. All timber (joisted) floors were rehung to reduce thermal bridging and eliminate the risk of condensation and rot on joists. Steel beams were hung in insulated pockets in the party walls at the front, middle and rear of each level. On the second and third floors, where existing floor joists were in poor condition, new floors were installed. On the first floor, the existing joists were propped and cut back from their pockets in the external walls before the steels supports were installed. The front and rear walls were tied to the steel beams with low thermal bridging wall ties. At the time, there was no manufacturer capable of producing high-performance, triple glazed windows suitable for use in the strict historical conservation area. The windows were required to look identical to the original doublehung sliding sash windows. In concert with a second project funded by the UK Technology Strategy Board, new triple glazed sash imitation windows were developed and manufactured. Although indistinguishable from the original windows from the exterior, these windows open with a tilt-and-turn mechanism to ensure airtightness. The front door was custom-manufactured in the same workshop. All walls were insulated internally, while insulation was provided between and below rafters on the roof and within the floor construction. All thermal bridges were addressed with individual details and the use of structural insulation where necessary. Room layouts were changed and the interior of the house was entirely redecorated. Metal spiral ductwork was run throughout the house for the combined ventilation and heating system. 3. Pictures of elevations Figs 2-4 (clockwise) Front elevation, solar thermal array, green roof

3 Fig 5 Rear elevation Fig 6 Front door 4. Sample interior picture Fig 7 Living room on first floor

4 5. Cross-section of implementation plan (Above) Fig 8 Renovation section [T. Macmillan-Scott]; (Below left) Fig 9 Section through rear area of house and kitchen; (Below right) Fig 10 Section through front area of house

5 6. Floor Plans Figs Floor plans [T. Macmillan-Scott]

6 Fig 13 Loft and roof plans [T. Macmillan-Scott] 7. Construction details 7.1 Construction and insulation of floor slabs Three distinct types of floor construction were used in the building. a) Under the basement floor: prototype labyrinthine heat exchanger constructed and provided with a screed to give a slope, 150mm PU foam installed over the heat exchanger and topped with a floating floor of marine plywood. b) On the suspended floor alongside the basement: joists lowered and rehung on joist hangers to allow installation of 200mm PU foam above the joists and a floating floor of tongue and groove chipboard. c) Below the kitchen floor: original concrete slab removed, 150mm PU foam installed over compacted hardcore and a 150mm concrete slab laid over the insulation, solid hardwood floor finish. Fig 14 - Insulation being installed in two layers over suspended floor Fig 15 - Structural insulation below floor joists over basement wall

7 The use of internal insulation greatly simplified the detailing of most floor-to-wall bridges. Internal walls over the floor constructions were avoided almost entirely and, where necessary, were installed over structural insulation to make the thermal bridge negligible. The most challenging detail was the connection between the basement wall and the suspended floor, which was cut off as detailed in Figs X and X. Fig 16 detail of connection between suspended floor and basement wall 7.2 Construction of exterior walls Exterior walls were insulated internally with the following build-up: - Existing brick (330mm on ground floor and basement, 220mm on upper floors) - Metal battens forming approximately 25mm cavity and straightening walls - 130mm phenolic insulation - 12mm OSB layer, acting as airtight layer and taped at all joints - 50mm phenolic insulation, grooved out to run services - 12mm plasterboard with skim finish In addition, party walls were insulated internally to cut off thermal bridges and provide protection from low heating levels in neighbouring properties, with a build-up as follows: - Existing brick (220mm) - Metal battens forming approximately 25mm cavity and straightening walls - 25mm phenolic insulation - 12mm OSB layer, acting as airtight layer and taped at all joints - 25mm phenolic insulation, grooved out to run services - 12mm plasterboard with skim finish By insulating all brick walls, it was trivial to intersect the insulation and prevent thermal bridges on corners. Internal walls were rebuilt inside the insulation layer and fixed into the OSB layer where necessary. All hangings and other fixings can safely be screwed into the OSB layer without compromising the airtightness of the building.

8 Figs (clockwise) first layer wall insulation, steel battens, insulation behind floor joists 7.3 Roof constructions The building contains both flat and pitched roofs, all insulated to the same specification: - 150mm phenolic foam in between joists/rafters (all ventilated from above) - 12mm OSB airtight layer - 50mm phenolic foam services layer - 12mm plasterboard with skim finish Fig 20 Installation of insulation over flat ceiling 7.4 Window specifications and installation The windows installations benefited from the existence of sash boxes from the original windows, where the counterweights for the sliding sash windows had been hung. By installing insulation within the sash boxes, it was possible to greatly reduce the thermal bridging around the frame of the window.

9 ls The windows were custom-manufactured for the project. The glazing has a centre-pane U-value of 0.58 and g-value of (Pilkington triple glazing with two low-e coatings). Frame U-values were calculated to have an areaweighted U-value of 0.94W/m 2 K and warm-edge spacers were used. (Above) Fig 21 Installation drawing for bay windows; (below left) Fig 22 New windows alongside original sash windows on neighbouring property; (below right) Fig 23 Thermal imaging of finished window [Alex Rice] 7.5 Airtightness A continuous airtight layer was formed within the insulation build-up of the house. This was formed of an OSB layer taped at all joints and running continuously within walls, under floors and over ceilings. The bright colouring and contrast of the tape helped to make the airtight layer very clear and all contractors onsite were made aware of its importance. Difficult junctions and services penetrations were carefully designed and drawings were provided to contractors where appropriate.

10 Fig 26 Air leakage test certificate 7.6 Ventilation ductwork Metal spiral ductwork was used throughout the building, of diameters between 100 and 160mm as appropriate. By integrating the design into the renovation work and using a combination of ceiling and floor grilles, it was possible to keep almost all ductwork runs inside floor voids or stud walls. There are a few areas where boxing has been installed, but this has been in keeping with the interior design of the house. The only area with significant intrusion from ductwork is the basement utility room (as shown). By keeping as many connections as possible exposed in this area, it is possible to reduce the complexity of the systems in the rest of the house. In addition, an external summer bypass is provided for the ventilation unit and a spring/autumn bypass is provided for the ground-to-air heat exchanger. Large silencers for the ventilation system are also shown. Figs Sketches of ductwork runs in main house and in basement

11 7.7 Ventilation central unit Ventilation was provided by a Passive House certified Genvex Combi 185L. The unit has the following characteristics: - Heat recovery efficiency = 76% - Fan electrical consumption = 0.31 Wh/m 3 (at 169m 3 supply air flow rate) Frost protection and additional winter pre-heating and summer cooling are provided by a prototype ground-toair heat exchanger constructed in a labyrinth pattern below the insulation of the basement floor. The system is designed as an alternative to standard earth tubes that is suitable for use in urban areas with restricted space. The original basement floor was covered with a new screed to slope the floor surface downwards towards a central drain carrying condensate to a sump in the centre of the room. Fig 29 Underground heat exchanger 7.8 Heat supply Heat supply is provided through the ventilation system by an air-to-air heat pump inside the combi unit. This is supplemented when necessary by a direct electric heating coil inside the duct. The air source heat pump also functions as an air-to-water heat pump, bringing domestic hot water up to temperature when the large solar thermal array does not provide sufficient heat. Figs Layout of heating supply and ventilation combi system 8 PHPP key results Specific space heat demand: 11kWh/m 2 a Pressurisation test result: 0.49ach@50Pa Specific primary energy demand: 72kWh/m 2 a Specific primary energy demand (excluding household electricity): 44kWh/m 2 a Specific primary energy conservation from solar PV: 8kWh/m 2 a Heating load: 9W/m 2 a In general, these results are comfortably within the Passive House guidelines. The milder climate of southern England helps both to reduce heat loss in winter and to limit the frequency of overheating in summer.

12 9 Construction costs 1,410 /m 2 usable area (calculated to PHPP guidelines), including all renovation work and building services. 10 Total building cost 275, Year of construction Original construction: c.1870 Renovation: Architectural design There was very little architectural input into the renovation project, with the exception of the revised floor plans. Generally, the architectural design was retained as built by the Victorian builders of the 19 th century. 13 Building services planning There was an ambition to provide all of the heating to the building with the lowest feasible environmental impact. In a medium-high density urban context, a building of this type has a very limited footprint. The project aimed to investigate how such buildings can provide nearly all of their energy requirements from this very limited footprint, limiting external inputs to the building as far as possible by using the ground, air and sunlight falling on the 80m 2 that the building occupies. The house is no longer dependent on gas supplies (except a negligible quantity used for cooking) and has no radiators, towel rails or underfloor heating installed. 16 Experiences At the date of writing, the house has not yet been occupied for a full year. As such, there is not yet sufficient data for a complete comparison. However, the metered energy use between January and June 2011 was 1.78MWh (including space heating, DHW, auxiliary and household electricity). Projected forwards, this gives an annual energy consumption of approximately 5.35MWh, or a saving of 89% against the most recent metered energy consumption from the house before the renovation works. The values above correspond to a Passive House specific primary energy demand of 54.8kWh/m 2 a. This is well below the predicted energy consumption, despite the presence of a baby and young child (and hence very intensive usage of the washing machine). Close monitoring of the house continues and it will be interesting to see if this performance is sustained over the coming years. The user experiences are overwhelmingly positive and the owner describes the house as a fabulous living environment exceptionally comfortable. 17 Existing studies and publications E.H. Borgstein, T.C. Pakenham and A.M. Raja Low energy retrofit of historic terraced dwellings CIBSE Technical Symposium, 2011 { HYPERLINK " }