Passivhaus The first 3 in the UK sally godber MEng CEng MIMechE www.peterwarm.co.uk
Intro to me/warm Mechanical Engineer Background in building services Set up WARM Jan 2009 Involved in 5 Passivhaus schools as designers & certifiers. 3 completed Oct 2011
What I m going to talk about What the standard is How it is applied to schools What is means for building design What it means for services design Some examples & lessons learnt from the three initial Passivhaus schools
Passivhaus a comfort standard? No draughts No cold radiant No summer overheating Fresh air always Whole building warm Fuel Poverty eliminated - all by simply improving the build quality
Passivhaus standard Air-tightness Surface temp (windows) Summer overheating Vent Heating 0.6ach @ 50Pa >17degC Max 10% >25degC ~5 l/s/person 15 kwh/m 2 yr @20C Primary Energy 120 kwh/m 2 yr Comfort Comfort Comfort Comfort Energy Energy
Typical UK schools internal environment CO2 >3,000ppm on a regular basis!
Typical UK schools energy use
Energy kwh/m2.yr 10 New UK Secondary Schools 400 350 300 250 200 150 100 120 50 0 Primary Energy 15 Heating Energy (Demand)
Building Design Step 1 - Form
Step 2 - Insulation
i.e. U ~ 0.15W/m 2 K
Step 3 - Windows
Best glass (U g = 0.5 W/m 2 K) and Average frame ( U f = 1.4W/m 2 K) Poor Installation; Traditional mullions Installation free of thermal bridges; Simplified design U window =1.8 W/m2K U window =0.8 W/m2K
Step 4 Air tightness & vent Not Good Enough!! Need to separate insulation & airtightness layers from services during design.
Very good, but no services!!
Ventilation Design: Good air quality Feels draughty & cold Reality: Feels warmer & less draughty Bad air quality Lots of Heating Energy Less Heating Energy
Passivhaus ventilation Airtight Heat recovery vent = Good Air Quality, feels warm and draught-free But what about energy consumption?
CO2/Cost Details are critical! Ventilation Energy Use 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Natural Ventilation Mechanical 50% 60% 70% 80% 90% 100% Heat Recovery Efficiency
Heating Very low load (typically 10W/m 2 ) Need to be careful not to oversize! Possible to simplify systems Controls need thought, not to complex!
Primary energy Once heating is sorted, all other energy uses need to be considered for true low energy design. Unregulated energy use included, key areas that need addressing are: ICT, particularly projectors Kitchen Sprinkler system Domestic hot water Lighting
Geometric thermal bridges 75mm conc 150mm insulation 150mm conc
>3mm!
Montgomery, Exeter Demand-control ventilation based on CO2 levels in each space Max vol flow sized for number of occupants (i.e. no increase due to hall etc) Separate WC & Kitchen AHU Mixed mode during summer Electric heaters in ductwork to each classroom DHW from heat pump with trace htg
Untested ventilation unit
Lessons learnt: Montgomery Occupants generally like it! Some teething problems with airflow & cooler air being supplied to the rooms Primary Energy so far ~150kWh/m2a, Zero-Carbon BMS unusable by school & submeters not commissioned. We see risk areas as being: Ductwork heaters mean vent must be on to provide heat Hot water trace heating & HP efficiency Ventilation performance SIP wall panels, care needed Door performance difficult to achieve Parapets are a massive energy drain
Oakmeadow & Bushbury Constant volume ventilation with central CO2 monitoring Designed so air is used more than once Separate toilet fan for the summer use Natural vent during summer months Standard wet htg & dhw from Gas boilers
Lessons learnt: Bushbury/Oakmeadow Min firing power of boilers = 25kW greater than average LTHW load =20kW Heating <15kWh/m2a with 22degC, surprising considering only controlled via weather compensation DHW losses estimated 60-70% of heat input AHU controls, auto bypass essential Kitchens cooking and dishwash as expected. No heating required in kitchens thanks to heat recovery on vent & good control. Lighting energy greater than expected, auto controls default on in many cases, 10+ hrs/day average. Sprinkler pump house heated! Seems to be running at 3kW through the summer, was 4kW in winter. ICT not as significant as predicted Primary Energy ~ 170kWh/m2a, lights and sprinkler frost heaters
Summary Attention to details! Ventilation easy to double energy use through poor control Glazing spec critical effects daylight, solar gain, thermal performance & comfort Insulation tea cosy (as far as possible)
Passivhaus Why it will deliver better schools in the UK Real low energy Excellent indoor comfort Sorts the fabric once and for all Reduces reliance on technology
So, what about the UK High electricity use = more gains, more overheating, more problems. Are we going to realistically get this down? PH schools demonstrate significantly lower PE but not as low as predicted ICT getting better all the time
Building Regs
Passivhaus Building Regs Total = 15kWh/m 2.yr Total = 54kWh/m 2.yr
Ventilation efficiency = (T extract T exhaust ) (T extract T inlet ) T extract T inlet T supply T exhaust
Measuring position Temp C Inlet 4.86 Supply 22.12 Extract 24.99 Exhaust 9.85 Supply efficiency 85.8% Exhaust efficiency 75.2% Plus duct runs to external as short as practicable
Space & water heating Primary Energy Electrical Energy
All add to heat gains = summer overheating = offset htg (i.e. hides construction defects) Cooling Fans, Pumps & Controls Electrical Consumption Lighting Server Catering Equipment Selection Control