Construction airtightness refers to the role of wind pressure and heat pressure, to ensure that the temperature within the building envelope system is constant, one of the important indicators, directly related to the indoor cold wind or hot air infiltration caused by heat loss, that is, indoor energy loss, the higher the airtightness level, the smaller the heat loss.
The number of pressure test air changes required in the passive house, i.e., airtightness n50 ≤ 0.6h-1, higher airtightness greatly reduces the indoor and outdoor air exchange, when heating in winter, high airtightness reduces the heat loss caused by cold air infiltration indoors and reduces the heating energy demand, and similarly, in summer when refrigeration reduces the infiltration of hot air from the outdoors and reduces the air-conditioning energy consumption. Of course, the airtightness is not the only indicator of reducing energy consumption, which also includes the conduction heat loss of doors, windows, walls and other components.
1 ? Airtightness design considerations
1.1 ? Airtight layer location and representation
The airtight layer is mainly composed of the building envelope, including doors, windows, walls, roofs, floors, etc. It is generally located on the inside of the exterior wall and continuously wraps the entire building envelope. In the design drawings, generally with a thick red line on the inside of the building envelope, but there is still part of the design of the airtight layer is missing, resulting in the construction personnel can not be clear about the location of the airtight layer, resulting in the construction of negligence and affect the effect of the passive house, as shown in Figure 1.
1.2 ? Common parts of airtightness measures
1.2.1 Passive exterior doors and windows
Hebei province engineering construction standard "residential building energy-saving design standards" (energy-saving 75%) in the window-to-wall ratio is clearly stipulated, and the southward window-to-wall ratio, for example, the window-to-wall ratio is as high as 0.5, so the windows of the airtightness of the building will have a significant impact on the whole building of the passive house, therefore the passive house is located in the outer perimeter of the external doors, external windows, and the windows of the passive house will have a significant impact on the building. The exterior doors and windows within the protection should meet the airtightness requirements in addition to the U-value ≤ 0.8w/(m?.k) required for passive house. The Ministry of Housing and Urban-Rural Development issued the "Passive ultra-low energy consumption green building technical guidelines" in October 2015, which stipulates that "the external doors and windows should have good airtightness, watertightness and wind pressure resistance, and their airtightness level should not be less than 8" Compared with the traditional building, the doors and windows of the passive house are all installed using external mounting. At the same time, the door and window frames and wall connection parts should adopt the measures of waterproof vapor barrier membrane (inside) and waterproof breathable membrane (outside) to avoid the risk of air or water leakage in the gap between the frame and the wall, as shown in Fig. 2.
1.2.2 Wall Masonry and Plastering
The Ministry of Housing and Urban-Rural Development has issued the "Code for Quality Acceptance of Decoration and Decoration of Buildings", which is the first standard in 4.2.4 of the "Code for Quality Acceptance of Decoration and Decoration of Buildings", and it has been adopted by the Ministry of Housing and Urban-Rural Development in 2001. 2001, Article 4.2.4 clearly stipulates: "Plastering works shall be carried out in layers. When the total thickness of plastering is greater than or equal to 35mm, strengthening measures shall be taken. Plastering on the surface at the junction of different material substrates shall take reinforcing measures to prevent cracking", and in the note, it is clearly put forward: "At the junction of different material substrates, due to the inconsistency of water absorption and shrinkage, the plaster layer on the surface at the junction is easy to crack, and all reinforcing measures shall be taken to ensure the quality of the plastering works in a practical way. " Therefore, in the passive house design, wall masonry and plastering should take airtightness safeguard measures to prevent wall cracking or plaster layer cracking due to uneven settlement or contraction of the wall, especially in the design of masonry plastering, should be clear in the design of anti-cracking measures, and to ensure that airtightness measures are firm and reliable.
Figure 1?Airtight layer labeling schematic
Figure 2?Doors and windows design node
Figure 3?Airtightness treatment
1.2.3 Integration of the enclosure structure
In order to ensure that the building enclosure structure of the airtight layer of the integrality of the design of the penetration of the external wall, roof, floor piping or pre-buried pipe should be taken. Airtightness treatment measures, such as Figure 3.
2 ? Airtight construction precautions
As the saying goes, "three parts design, seven parts construction". Whether the passive house can ultimately achieve the goal of energy saving, the refinement of construction plays a decisive role.
2.1 ? Doors and windows installation project
Passive house external doors and windows are used for external installation, the outer side of the pad wood and special corner code for fixing, inside and outside the two sides of the waterproof vapor barrier film and waterproof breathable membrane membrane were used for pasting sealing, cumbersome processes lead to more prone to airtightness hidden trouble, the following issues should be noted:
(1) in the construction of waterproofing membrane on the inner and outer sides of the corner of the door and window and the corner of the corner code, pad wood, the part of the paste is more difficult, therefore, this is more likely to occur. Part of the paste is more difficult, so this part needs to be set to strengthen the layer, in which the outer waterproofing membrane should be pasted sequentially from the bottom up to ensure that the lap part of the openings face down to reduce the potential risk of water ingress.
(2) in the paste waterproof membrane, to ensure that the grass-roots level is completely dry, to avoid waterproof membrane paste due to wall moisture is not firm.
(3) in the rainy season construction, for the external wall surface, especially around the door and window openings should be used waterproofing mortar for leveling, to prevent the rain long time wash the wall leading to rainwater seepage to the waterproof membrane, affecting the quality of paste.
(4) for non-self-adhesive waterproof vapor barrier membrane and waterproof breathable membrane, the construction method is simply summarized in four words: stick, paint, scrape, pressure, that is, first of all, waterproofing membrane adhesive in the window frame, and then special glue to "S" shape coated in the wall, and then the glue will be uniformly scraped, and finally will be pasted, and compaction of the membrane. It is worth noting that, in the glue scraping level, to ensure that the glue can continuously open.
2.2 ? Concrete engineering
When pouring concrete, ensure that the concrete is vibrated densely to avoid honeycomb, pockmarked and other quality defects. After the concrete is demolded, the formwork should be airtight sealing of the casing of the tie bolts. Since the tie bolts are set more often, it is easy to miss, so make sure to seal all the casing to avoid losing a lot due to small losses.
2.3 ? Masonry, plastering project
In the construction of masonry structure, masonry shrinkage cracks, cracking and other factors should be fully considered, strict control of block selection, age, mortar fullness, masonry height, etc., in order to autoclaved bricks and concrete bricks, for example, because of its early shrinkage value is larger, so it is required to be put into use after 28 days of age, such as the block itself there are defects such as breakage, cracks, etc., on the masonry strength, will produce Adverse effects, crack phenomenon will occur. When masonry, strictly control the thickness and fullness of the masonry mortar, as well as the daily masonry height and the slanting time of the gap between the top of the infill wall and the main structure.
The plaster layer can constitute an airtight layer and can also make up for masonry defects in the wall, so it is also necessary to take anti-cracking measures when plastering, especially at the intersection part of the two materials, and it is necessary to take anti-cracking measures, such as hanging nets.
Because wall cracking will have a great impact on the overall airtightness of the building, therefore, in the masonry and plastering process, full consideration of wall cracking factors, to minimize the risk of wall cracking, in order to ensure the maintenance of the structure of the airtightness.
2.4 ? Installation engineering
Passive house airtightness in the design stage, construction stage need to pay attention to airtightness problems, and often ignore the use of the stage of airtightness problems. Here only to the floor drain, washbasin as an example, in the passive house project decoration is completed when the airtightness completion test, the floor drain, washbasin and other parts of the most prone to air leakage phenomenon, and the national standard GB50015 "Building Water Supply and Drainage Design Specification" in 4.5.9 and 4.5.10 respectively, the provisions of: with a water seal of the floor leakage depth of the water seal shall not be less than 50mm and give priority to the use of the function of anti-drying Floor drain. However, I believe that, due to a long time without the water seal is easy to dry up, and with the anti-drying floor drain after long-term use of the rebound function deterioration and other issues, resulting in pipeline odor still into the room, so there is a need to set up permanent and not be disturbed by external airtightness measures.
3 ? Airtightness testing and evaluation
Using the "blower door method" to identify a passive house or a passive house and retrograde pressure test. The blower is installed on the door or window opening located on the exterior envelope, and other non-permanent openings in the room are blocked. A micro-positive and micro-negative pressure of 50 Pa was successively established and the volumetric flow rate of air pumped by the fan at that air pressure was measured.
It is worth noting that the larger the building is, the easier it is to achieve the requirement of n50≤0.6h-1. In fact, large buildings with n50 up to 0.6 may still have a large number of air leaks, so for large passive buildings, i.e., when Vn50≥4000m?, both the number of air changes per hour (n50) and the building permeability (q50) are tested, and q50 should be be less than or equal to 0.6m?/(h.m?).