Low Energy HousingAn Overview

Dr Nick Kelly

Energy Systems Research Unit (ESRU)

Mechanical Engineering

University of Strathclyde

Content

• Housing and Energy Consumption

• Legislating for Better Performing Housing

– What is a Low Energy House?

– PassivHaus

• Zero Energy/Carbon Housing

– Case Studies

– Simulations

• Implications of Zero Carbon Housing

– LV Network

– Heat Networks

Housing and Energy

• The domestic sector in the UK accounts for

almost 37% of final energy consumption

• The majority of energy consumed is for space

and water heating, not electricity

• The energy efficiency of the bulk of the housing

stock is poor with an average SAP rating of 52

[scale of 1-100]

• Generally the older the building the poorer the

energy performance: ~70% of the UK housing

stock is pre-1970

• There is significant scope for energy efficiency

improvements with savings in space heating of

up to 90% achievable

Improving Energy Efficiency

• There have been various pieces of EU-wide legislation

to improve the energy performance of housing (and

buildings in general) in an attempt to mitigate their

GHG emissions

– Energy Performance in Building Directive (2002)

– Energy Efficiency Action Plan (2006)

– End-use Efficiency and Energy Services Directive (2006)

• These have been implemented at a sub-national level

through mechanisms such as the building regulations

(England, Scotland, Wales and Northern Ireland)

• The UK has been active in developing its own targets

(Energy White Papers 2003, 2007), Climate Change

Act (2008); all made clear that radical improvements in

domestic energy efficiency was key to achieving deep

carbon reductions (80% by 2050)

Improving Energy Efficiency

• The EPBD was a

milestone in energy

conservation legislation

and set out minimum

energy performance

targets for buildings

• Many EU member

states have gone

beyond the EPBD and

set out their own criteria

for low-energy buildings

Austria Low energy building defined as annual heating energy consumption below 60-40 KWh/m², 30 % above standard performance. Passive building defined as 15 kWh/m²

Belgium (Flanders) Low Energy Class 1 for houses: 40 % lower than standard levels, 30 % lower for office and school buildings. Very low Energy class: 60 % reduction for houses, 45 % for schools and office buildings.

Czech Republic Low energy class: 51 – 97 kWh/m2 p.a. Very low energy class: below 51 kWh/m² p.a., also passive house standard of 15 kWh/m2 is used.

Denmark Low Energy Class 1 = calculated energy performance is 50% lower than the minimum requirement for new buildings Low Energy Class 2 = calculated energy performance is 25% lower than the minimum requirement for new buildings (i.e. for residential buildings = 70 + 2200/A kWh/m² per year where A is the heated gross floor area, and for other buildings = 95+2200/A kWh/m² per year (includes electricity for building integrated lighting)

Finland Low energy standard: 40 % better than standard buildings France New dwellings: the average annual requirement for heating, cooling, ventilation, hot

water and lighting must be lower than 50 kWh/m² (in primary energy). This ranges from 40 kWh/m² to 65 kWh/m² depending on the climatic area and altitude. Other buildings: the average annual requirement for heating, cooling, ventilation, hot water and lighting must be 50% lower than current Building Regulation requirements for new buildings For renovation: 80 kWh/m² as of 2009

Germany Residential Low Energy Building requirements defined as 60kWh/m² or maximum energy consumption. Passive House standard defined as 40 kWh/m² buildings with an annual heat demand lower than 15 kWh/m² and total consumption lower than 120 kWh/m²

UK (England & Wales) Graduated minimum requirements over time: 2010 level 3 (25% better than current regulations) 2013 level 4 (44% better than current regulations and almost similar to

PassivHaus) 2016 level 5 zero carbon for heating and lighting. 2016 level 6 zero carbon for all uses and appliances.

UK (Scotland) Graduated requirements over time (Sullivan, 2008): 2010 a 30% reduction in regulated energy uses (excludes appliances); 2013 a 60% reduction(proposed); 2017 a 100% reduction (proposed); and zero lifecycle carbon buildings by 2030 (proposed).

PassivHaus• The PassivHaus standard is gaining popularity

around Europe as a benchmark for energy

efficient buildings

• The requirements for a Northern European

PassivHaus are:– very high levels of insulation (wall U-values less than 0.15

W/m2K);

– high-quality building construction (thermal bridge free, air-

tightness of construction better than 0.6 air changes per

hour [ACH] measured at 50 Pa with ventilation openings

closed, equivalent to 0.03 ACH under normal conditions);

– high-performance glazing (U-value less than 0.85 W/m2K

including installation, frame and glazing edge losses, solar

transmittance greater than 50%);

– a high efficiency ventilation system with heat recovery

(MVHR);

– construction mass, ventilation openings, thermal capacity

and shading designed for comfortable summer

temperatures; high efficiency appliances and lighting.

Zero Carbon Housing

• The PassivHaus standard focuses

on reducing energy demand

• Whilst microgeneration can be

integrated with a PassivHaus their

contribution is not counted

• A step beyond PassivHaus is to

offset the energy demand of the

building using local zero-carbon

generation

Zero Energy/Carbon Housing

• What does zero energy or zero carbon mean? There are multiple

definitions:– Autonomous Zero Energy Buildings – all demand are met by on-site

generation, no external network connections

– Net-zero site energy – local generation completely offsets on-site demand,

demand and supply are not temporally matched but balance over a year

– Net-zero source energy - local generation completely offsets primary energy

demands, demand and supply are not temporally matched but balance over a

year

– Lifecycle net-zero energy buildings - local generation completely offsets

primary energy demands AND embodied energy, demand and supply are not

temporally matched but balance over the lifetime of the building

– NB For a building to be zero carbon (as opposed to just zero energy) then the

local generation needs to be carbon free: e.g. PV, solar thermal, biomass,

SWEC

Zero Carbon Housing Standards• England and Wales have been one of the first areas in Europe to develop

specific zero carbon standards for new homes

• Code for Sustainable Homes (CSH) (DCLG, 2008a) defined voluntary levels of performance (Codes 1 to 6)

• Two of these levels are described as zero-carbon buildings: – Code 5 equates to a 100% reduction in regulated energy use, with these

being offset by renewable heat and power generation. Energy use from appliances is not offset (so-called unregulated energy use).

– Code 6 proposed zero-carbon for all energy use including appliances by 2016. This equates to a 140% reduction in calculated regulated energy uses such as heating and cooling (i.e. 100% reduction in regulated energy use plus 40% from local electrical generation technologies such as PV to offset the unregulated energy use by appliances)

Zero Carbon Housing Standards• To encourage the development of a zero-

carbon housing market, the UK Government

has announced a tax incentive for new zero-

carbon buildings to become effective in 2016

• There is also a feed-in tariff (FIT) for small-

scale renewable electricity generation and a

proposed renewable heat incentive (RHI) to

replace the defunct low-carbon building

programme

• Technologies covered under the FIT include

PV, CHP and SWECs

• Note there is growing doubt as to whether the

RHI will actually appear

Supply TechnologiesElectrical Thermal

Despatchable

Non despatchable

SWECS PVSolar

thermal

Heat Pump

CHP

Micro-hydro

Biomass boiler

Supply Technologies

Supply Technologies

Supply Technologies

Supply Technologies

Supply Technologies

Supply Technologies

ZCH: Examples

BedZED, UK (2002)• The Beddington Zero Energy Development

(BedZED) project in Hackbridge, London was an attempt to create a zero-energy community

• Consisted of 99 super-insulated dwellings of various sizes, workspaces and community facilities.

• on-site zero-carbon generation provided by a prototype 120kWe wood-waste fuelled combined heat and power (CHP) system with 777m2 of photovoltaic panels

• designed to meet all of the energy demands of the residents along with providing the potential to power up to 40 electric vehicles at some future date.

ZCH: Examples • Monitoring indicated:

– that space heating demand was 90% lower than the UK average

– electrical power consumption for appliances and lighting was 33% lower than average, however this was still higher than anticipated due to residents using back-up electrical water heating

• The development did not achieve zero-carbon operation, primarily due to the fact that the prototype biomass CHP system was unreliable and never operated effectively (it was shut down in 2005)

• The remaining PV system only offset around 20% of the total energy demands of the community with the remainder being drawn from external supplies

ZCH: Examples

Portland House, Australia (2009)• Demonstration family dwelling in Portland Victoria

with a super-insulated and tightly sealed fabric, thermal mass and a cooling tower (promoting stack ventilation) for summer cooling

• All appliances in the dwelling were low-energy

• Energy was provided by a 1.4kW PV installation and 3 solar thermal panels augmented with an electric back-up heater were used to meet the dwellings’ hot water demands

• A reversible heat pump met the dwelling’s small space heating and cooling requirements.

ZCH: Examples • Monitoring over the period September 09 to June 10 indicated that the PV

installation provided 93% of the dwelling’s electrical energy consumption

• Note that this period did not cover all of the winter months and it is likely that the quantity of imported electricity will be slightly greater over the course of a full year.

• The developers have since indicated that the PV installation is due to be doubled in size to a capacity 2.8kW. Given the current performance, this is likely to turn the building into a net electricity exporter.

ZCH: Examples

Wheat Ridge, Colorado (2005)• The Habitat for Humanity home in Wheat Ridge,

Colorado is a 119m2 super insulated dwelling e.g. the building features low-e solar glass with argon fill and a U-value of 1.14W/m2K

• Renewable heat provided by a 9m2 solar collector with a 760 l thermal store, backed up by a gas-fired water heater

• Renewable electricity provided by a 4 kWp roof-top PV system

• The building also features a mechanical ventilation system with heat recovery.

ZCH: Examples • Monitoring indicated that during the period April 2005 to the end of March

2007, the PV system produced an excess of 1542 kWh

• Gas consumption for the water heater amounted to some 1670 kWh.

• The net site energy requirement for all fuels of the home was approximately 0.6 kWh/m2/year.

ZCH:Lessons?• From the evidence of the case studies achieving

zero-carbon operation is not straightforward!

• A building designed to be zero-carbon does not necessarily perform as zero carbon

• Most fail to achieve this due to 1) under-prediction of demands at the design stage 2) over-prediction of energy yields from renewables or 3) poorly performing equipment in-situ

• PV seems to be the ubiquitous option for electricity generation

• Most achieve significant reductions in thermal demand … less success with curbing electrical and demands

ZCH: Simulating Performance • In addition to data emerging from the limited

number of demonstration “zero-carbon” buildings simulation can provide useful performance information

• This study investigated a typical detached dwelling with a floor area of 136m2. The building was assumed to be occupied by a family of 4 in which the parents work;

• Occupancy was therefore intermittent;

• The building performance was assessed for a Scottish West-coast climate.

• NB The mechanics of building simulation will be covered in more detail in the next presentation

ZCH: Simulating Performance • modelling indicated that for the detached

house to achieve the 140% reduction target as set out in the Code for Sustainable Homes required the following measures:

– 46m2 PV electrical generation (approx 6 kWp)

– passive house building envelope

– high efficiency mechanical ventilation heat recovery (MVHR)

– 4m2 Solar thermal panels

– 2kW Biomass heating

– high A+ rating efficiency appliances

– high efficiency lighting

ZCH: Simulating Performance • To illustrate the change in energy performance of housing, a comparative

simulation was undertaken with the proposed zero-carbon house and a more conventional dwelling (built in UK post 1997)

• Dynamic simulation of the building energy flows over a 1-year period @ 10 minute time intervals, west coast climate (solar radiation, temperature, wind speed, wind direction), pre-defined occupant and equipment heat gains, control settings (on/off times, set point temperatures), etc.

• Produces large volumes of time series data: temperatures; heat fluxes, electrical production (PV), etc.

Base Case Dwelling Zero Carbon Dwelling External walls W/m2K 0.45 0.11 Floor W/m2K 0.6 0.10 Ceiling W/m2K 0.25 0.13 Glazing W/m2K 2.10 0.70 Average uncontrolled infiltration ACH

0.5 0.031

Heating Gas boiler + radiators Biomass boiler + heating coil in MVHR

1 Model includes mechanical ventilation heat recovery (MVHR) with average efficiency of 90% providing 0.4 air changes per hour (ACH).

ZCH: Simulating Performance

ZCH: Simulation Results • Aggregating the data from the simulation gives the following annual

performance characteristics

Base Case Dwelling Zero Carbon Dwelling Heating demand kWh 3083 372 Hot water heating demand kWh 2342 1850 Electrical Demand kWh 5776 3240 Total Demand kWh 11201 5462 PV Output kWh - 5023 Solar Thermal Output kWh - 1709 Biomass boiler Output kWh - 1172 Total Production kWh 7904

ZCH: Simulating Performance

ZCH: Analysis

• Dramatic reduction in demand for space heating, dropping from 3083 to 372 kWh• The heat-to-power ratio of the simulated dwelling shifts from 1:1 in the base case dwelling to

0.7:1 in the zero carbon dwelling • The calculated electrical demand reduces from 5776 to 3240 kWh (due to the adoption of

high efficiency appliances)• The modelled electrical demand for the zero carbon dwelling also indicated a drop in peak

demand of around 10% • The addition of 6kWp of PV generation to the simulated dwelling gives rise to striking

seasonal variations in electrical energy flows: in winter 768 kWh of electrical energy is imported, whilst in summer a total of 1,756 kWh if exported to the network

• There are also significant daily variations. For example, on an average summer day, a peak electrical demand of 4 kW occurs in the morning. By mid-day this has changed to a peak electrical output of 5 kW

• The variability in solar hot water production is as pronounced with 40kWh produced by the solar collectors in January, offsetting around 18% of the total thermal demand compared to 219kWh in June, which exceeds the total thermal demand in the zero carbon dwelling.

ZCH: Analysis

Implications?

• The dramatic reduction in demand for space heating raises questions as to how space heating could be provided in future dwellings.

– Often in current UK dwellings, low space heating demands in premises such as flats have tempted developers to install low-cost technologies such as electric resistance heating or storage heating.

– Any move to electrically-based heating technologies will further change the energy demand patterns of zero carbon dwellings as heating energy loads are displaced from the gas grid to the electrical grid

• Thermal energy demands for the zero carbon dwelling shift from space heating to hot water

– This offers an opportunity for load shifting with regards to when heating is provided – a particularly useful feature if those thermal loads were met by cogeneration, heat pumps or direct electric heaters - enables a high degree of control over heating-related electrical loads and/or generation.

Implications?

• The low overall heating demand seen in the zero-carbon house also raises some serious questions regarding the development of heat networks (e.g. zero-carbon district heating schemes).

• The very low heat requirements make the prospect of heat distribution unlikely in all but the highest density housing developments such as flats: elsewhere the small revenue from heat sales per dwelling would be unlikely to offset the capital costs associated with the installation of metering, piping, heat sources, thermal storage and other balance of plant.

• The heat-to-power ratio of the simulated dwelling shift from 1:1 in the base case dwelling to 0.7:1 in the zero carbon dwelling.

• This seems to favour lower heat-to-power ratio equipment such as bio-fuelled internal combustion engines or (in future) fuel cells

Implications?

• Electrical energy becomes the predominant demand in the dwelling - currently over 80% of demand is thermal energy

• The reduction in electrical demand in zero-carbon houses is less dramatic than is seen for thermal demands, with in the case examined here.

• The modelled electrical demand for the zero carbon dwelling also indicated a drop in peak demand of around 10%

• Using a large areas of roof-mounted PV could lead to power management problems in climates with the highly variable daily and seasonal solar insolation levels such as those seen in the UK.

Conclusions

• To curb carbon emissions from dwellings building standards are being tightened leading to the development of a raft of low-energy building definitions

• In Europe, the Passive House standard is seen as a reference for low-energy buildings and has been demonstrated to reduce space heating demands by up to 90% (compared to conventional dwellings)

• Zero-carbon and zero-energy building standards are beginning to emerge such as those defined in the UK’s Code for Sustainable Homes

• There are different definitions as to what constitutes a zero-carbon or zero-energy building; the most common definition appears to be net-zero-source-energy where on-site renewable sources are used to offset a building’s primary energy demands.

• There are numerous examples of zero-carbon demonstrations throughout Europe and North America.

• Monitoring of actual performance indicates that most do not actually achieve zero-carbon operation.

Conclusions

• Zero-carbon buildings will have radically different energy demand characteristics compared to existing housing.

– space heating demand is minimal– electricity for appliances and lighting becomes the major energy demand

• In Northern latitudes there are very significant seasonal variations in PV electrical production the high levels of export to the network in summer could result in significant power management problems in areas with high levels of PV penetration.

• Significant swings from export to import were also evident throughout the course of a day.

• The change in the primary thermal demand from space heating to hot water provision affords opportunities for significant demand/supply control opportunities if adequate hot water storage is provided and if some of the heat demand is met by heat pumps or micro-cogeneneration devices.