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Passivhaus buildings provide a high level of occupant comfort while using very little energy for heating and cooling, leaving other topics for designers to decide whether they should be included or not.
Outline Specification of the Passivhaus Standard
The Passivhaus standard is a comprehensive low energy standard intended primarily for new buildings. The following energy performance targets define the standard and must be met in order for certification to be achieved.
|Energy performance targets and air changes per hour|
|Specific Heating Demand||≤ 15 kWh/m2. yr|
|Specific Cooling Demand||≤ 15 kWh/m2. yr|
|Specific Heating Load||≤ 10 W/m2|
|Specific Primary Energy Demand||≤ 120 kWh/m2. Yr|
|Air Changes Per Hour||≤ 0.6 @ n50|
The standard requires that the Primary Energy demand target is met in all cases, this figure must include the space heating, domestic hot water, lighting, fans and pumps and also all of the projected appliance consumption.
In addition to the primary energy demand the standard permits that either the Specific Heating Demand or the Specific Heating Load must be met.
The energy balance of the proposed building must be verified using the Passive House Planning Package (PHPP) using the appropriate regional climatic dataset. Either the monthly or the annual method may be applied.
If the Specific Heat Demand is ≤ 8kWh/m2.yr or the ratio of free heat gains to heat losses is greater than 0.70 it is recormended that the monthly method is used to ensure accuracy.
The standard provides limiting backstop values for the glazing specification, ventilation system, air tightness levels and thermal-bridging as these factors should not exceed these limits in order that the thermal comfort criteria can be maintained.
The following table illustrates the elemental backstop values which should not be exceeded in order for the Passivhaus certification criteria to be met.
|Design Component||Limiting value|
|Walls, Roof, Floor (U-values)*||≤0.15 (W/m2K)|
|Glazing unit||≤0.8 (W/m2K)|
|Installed glazing||≤0.85 (W/m2K)|
|Infiltration (ach-1)||≤0.6 @ n50|
|Thermal bridging (linear ψ value)||≤0.01 (W/mK)|
|MVHR coefficient (η HR)||≥0.75|
|Ventilation electric limit||0.45 Wh/m3|
|Appliances||High efficiency recommended|
|Lighting||High efficiency recommended|
|On site renewables||No requirement but SHW typical|
*please note opaque U-values are only recommended targets and are not critical to certification
The backstops above apply to moderate weather regions only, for warmer climates the performance values could be reduced. Please consult your building certifier for more information.
Comparison Passivhaus versus Code for Sustainable Homes
One can not directly compare the Passivhaus standard with the Code for Sustainable Homes. Passivhaus is an energy performance standard whereas the Code is an environmental assessment methodology covering the overall environmental performance of a building including for example construction site management, consideration of the materials used in construction, water consumption of the building, provision of recycling bins etc. The Passivhaus methodology is a tried, tested and successful approach to designing and constructing very low energy buildings, with thousands of examples built over the last 20 years all over Europe. The energy performance and carbon saving criteria of the Code for Sustainable Homes are based on SAP. Choosing between PassivHaus and the Code for Sustainable Homes can be a difficult choice, as making the wrong choice could infer costs not required for the development. Thir13en is available to assist in this regard.