Building Services

We’ve picked these ten points out to help design and construction teams on their way but always check with your Certified Passivhaus Designer or Passivhaus Certifier on applicability for your project….

1. Air handling units should be Passivhaus Certified or there is a 12 point penalty on the unit efficiency (but you knew that!) What you might not know is that for larger commercial units with flow rates above ~10000m³/hr there is no certification, but don’t worry, a certificate can be obtained through your Passivhaus certifier reasonably quickly and efficiently by the Certified Passivhaus air handling unit manufacturer providing the appropriate test data.
2. For ventilation of Passivhaus school (and other commercial) kitchens, 18% can be added to the efficiency of the air handling unit. If it is Passivhaus Certified this takes the total close to 100% (ie heat loss via the air handling unit can be ignored), but if it is not Passivhaus Certified 18-12 = 6% can be added. This is because much of the work of the kitchen air handling units is to remove excess heat.
3. Intake and exhaust ducts are cold in winter and need to be insulated with a vapour impermeable insulation, continuous from the air handling unit to the building envelope and sealed to the airtight layer of the building. Supply and extract ducts are at approximately room temperature and do not need to be insulated.
4. Passivhaus ventilation systems need to be commissioned according to Passivhaus requirements with operational pressures and noise levels measured. Total external pressures (duct losses) should be within the range on the Passivhaus certificate and noise levels limited to <30 db(A) ie less than the requirements of BB93 and has to be demonstrated on commissioning.
5. Radiators can be small as they do not have to drive convection against down drafts from windows. In classrooms they can be situated behind classrooms doors, with control by a simple TRV on the radiator.
6. Domestic hot water energy use can be high due to system losses. This is usually minimised by using distributed electric water heaters combined with small diameter pipework (10mm) running from a manifold to each hot water outlet. These pipes do not need to be insulated.
7. In the kitchen the domestic hot water is often on a secondary circulation system. Quality insulation of this pipework is essential. There should be no exposed metal. Get something into the specifications along the lines of:

Secondary circulation pipework is to be thermally insulated with continuous insulation of ## mm thickness and ## W/mK thermal conductivity or equivalent. There should be no exposed pipework – continuous through walls and with thermally broken clamps and hangers. Sufficient spacing must be allowed between pipes to allow for all round insulation.

8. School lighting design should aim for an average installed lighting load of 5W/m²
9. For access and security use battery operated access control wherever possible instead of mains operated maglocks.
10. Sprinkler systems can use and waste a lot of energy, especially due to poorly considered frost protection strategies. However, the energy usage of the sprinkler system does not have to be accounted for in the PHPP model. We always review the designs and do what we can to minimise energy usage.

If you would like a full copy of our working advise document for Building Services for Passivhaus schools please email us