Nico Paulin

Energy efficiency of domestic sector in Ireland

Aims

• Reducing energy demand in domestic sector

• Value of Irish building energy rating

• Retrofitting or Building from new

Objectives

• Finding out about climatic considerations

• Investigating most efficient systems

• Comparison of market between Irish and (rest of) Europe

Acknowledgement

Many thanks to Duncan Stewart for attending an interview to share his knowledge on the current trend of passive systems in Ireland.

The development of section 5 was strongly influenced by the interview.

Important

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Preface

Energy prices are constantly rising and utility bills are sometimes too much to handle for pensioners and low income earners. To reach a reduction in energy consumption, dwellings must apply passive systems in order to make a good use of the solar energy available throughout the year. This document investigates the situation of the Irish domestic dwelling market in comparison to the German standard. It focuses on the method of harnessing of solar radiation as well as insulation within dwellings envelopes.

Introduction

Since the early 1900s fossil fuels has been relied upon globally. This has underlined the need to develop substitute energy sources to meet the increasing demand. Renewable energy defines the start of a new chapter, and although it might be recognized as a new set of technologies, it reflects on ancient methods of harnessing energy. These technologies need to be used to establish a suitable environment within the society. The Earth approximately receives 9.1667 x 10^24 J of energy a year due to the sun [1], and it is therefore essential to use this energy in the right manner to reduce the daily energy consumptions.

In 2011, the household sector alone consumed 3,242 ktoe (tonne of oil equivalent) which equates to 3.77 x 10¹⁰ kWh. This has a share of 25% on the final energy demand of Ireland. Within this 25%, heating takes up the largest part with auxiliary electricity uses following up. For the final energy consumption in Ireland to decrease, individuals must benefit from energy efficient method to cut down on energy demand. [2]

An interesting approach to this issue is passive solar design. It is a term used when describing an entire building as a collector and storage system. The concept is to harness sun light during the day and release it as a form of heat at night when no sun light can be gained. A passive solar design can benefit from natural resources and maximize heat transfer within a building. Passive solar design is not a recent idea and in fact has been approached by Western ranch houses facing extreme sun light during summer seasons. They developed southward exposure with shady features, and local heat-efficient building materials. What is interesting about a passive solar house is its life cycle. Once built it requires very little maintenance and is therefore an advantage for the occupants.

Figure 1: Total Energy Demand by Sectors in Ireland

In 1996 the PassivHaus Institute in Germany set a building standard where any dwellings meeting certain criteria would be certified as ‘Passive House’. A passive house should deliver and maintain a pleasant temperature in the winter as well as during the summer with very little use of active heating or cooling systems [3]. It is important to understand the difference between a passive solar house and a passive house as the two terms describe different criteria. A passive solar house uses solar radiation to generate heat across the building. A passive house maintains temperature with the use of insulation and airtightness. Some of the basic requirements are listed below in Table 1 for Super Insulation.

Passive Solar House

• • No certification or regulation

  • Utilises sunlight to gain heat

  • Utilises thermal mass to absorb heat

  • Utilises thermal mass to release heat

Passive House

• Certified building

• Utilises insulation to retain heat

• Utilises airtightness to retain heat

• Utilises ventilation to distribute heat

  • May incorporate passive solar design

Table 1: Passivhaus Standard in the Irish Climate

U-values represent the heat transfer coefficient of a material or an element. It measures the rate of heat transfer through the element per degree of temperature difference between the internal and external environments [4]. The lower the U-value the better the building is insulated.

Before attempting to investigate the potential of passive solar design in the Irish market, the subject needs to be broken down into sections to evaluate requirements for a passive solar house. As mentioned above, a passive house relies entirely on solar energy, and depending on the location, the season and the weather conditions different designs are required. In order to harness, store and distribute energy, systems have been developed over the years. A passive solar house usually has a multiple number of systems installed within the building to facilitate the processes. Section two discusses several key systems which influence efficient passive design.

Case Study

Passive Solar House

The first influential passive solar house in Ireland was established in 1983 in County Dublin. The house was then monitored for the next 6 years to evaluate the energy consumptions at different period of the year. The house featured a ventilation system and solar collectors assisting the annual energy input. With the 110 m² south facing wall and the large glazing, the Garristown house was a successful collector of radiation. However the lack of resources and building development meant the house had poor insulation and therefore could not retain the heat efficiently. [5]

Figure 2 The Garristown Passive Solar House [5]

Passive House

One of the first passive houses built in Ireland was in 1991 by Scandinavian Homes Ltd. At the time their houses were seen as radical projects and the public were not convinced it could be the solution. The main reason was the high construction costs. It was too early to tell whether instrumental savings could be made. In 2010, Scandinavian Homes Ltd built the most efficient house in Ireland situated in Galway. This house, later named Hibernia, was constructed of Swedish timber frame which allows better insulation than maso nry during the winter. A timber house is durable and does not cost more than a masonry house to build. Hibernia has excellent ventilation systems circulating the heat around the house for an ideal envir onment. The insulation is improved by the use of an addition of triple-glazed windows letting in plenty of heat during the day and preventing it from escaping. Hibernia is fitted with under-floor heating through out the house which is usually switched on in the evening time during the winter. Heat panels are located on the south-facing roof providing enough energy to heat up 400 litres of water. Hibernia can achieve a daily heating cost of 77.6 cents at 9.70 a unit setting a new standard of energy preservation [6]. The open plan set up on the south facing rooms provides sufficient heat which can be transferred to the rest of the rooms via convection and conduction.

Figure 3: Hibernia, first passive house in Ireland (Galway) built by Scandinavian Homes Ltd.

Climatic Considerations

Location, Conditions and Season

Not all parts of the earth are subjected to the same solar radiation. Since a passive solar design utilises solar energy, it is important at this stage to find out how much energy can be harnessed in Ireland. A house on the equator will have significantly more solar radiation than one on the 90 degree North or South of it. This can change the design of a house as one might need a cooler environment in comparison with the other. Central Africa receives up to 2500 kWh/m2 of radiation per year where as Ireland located at latitude 53°3 0'00 N has a relatively low rate of 800 to 1100 kWh/ m² of radiation [7]. On a bright sunny day typically in June or July in Dublin, 4770 W of energy can be harnessed per square metre while 450 W in December [8]. Intensity of sunlight can vary due to the location, the weather condition and the season. The regular cloud formation covers Ireland over 50% of the time reducing so lar irradiation [9]. This can affect direct heat gain and photovoltaic systems such as water heating solar panels.

Figure 4: Ireland solar Irradiation [7]

Orientation of facade

The most important factor of passive solar design is the orientation of the building. In the northern hemisphere a building must have most of its windows and living spaces on the south-facing wall in order to collect as much light as possible during the day, while in the southern hemisphere, walls must be facing north. During the summer the sun’s position is higher than the winter which leads the light into different area of a house. This has to be calculated so that winter sun can be fully harnessed when most needed. Figure 5 illustrates the change of elevation of the sun during different seasons. A passive house would take that into consideration and make sure maximum sun can be gained during winter seasons. Glazing orientation can be an such as angled glazing like skylights as they have exposure to weather patterns and can directly affect temperatures within a building. Vertical glazing are commonly used as they can benefit from different weather conditions when appropriately shaded.

Figure 5: Annual Sun Position [13]

Systems

A passive solar house harnesses, stores and distributes energy with the use of passive or active systems and only requires 70 kWh/m² year of energy for heating [10]. This is due to the excess sunlight received during the day and the superior insulation which keeps the heat inside the house longer during the night. Systems can be incorporated in a house to maximise the energy efficiency. Many energy efficient systems have become very popular in the construction sector as they consume very little external energy. This section introduces key systems which have been used in passive solar houses and which could significantly improve the energy efficiency of a house with respect to the weather condition and its amount of irradiation. Solar thermal systems are either built using active or passive solar energy to gather and transform energy to heat [11].

Direct-Gain heating

Day lighting is a term describing natural light in a passive house. The use of day light is unfortunately forgotten sometimes but in reality it is of great importance in a passive solar house as it reduces the daily energy use. Deep windows must be installed for sun light to penetrate into the centre of the house. This is probably the simplest approach of passive solar heating. The idea is to have direct entry of solar radiation introduced into living spaces throughout the day to provide a higher room temperature and abrighter space [12]. With the use of energy absorbing materials in walls and floors, solar radiation can directly heat a building. This heat can then be released back into the room during the night when the sun is down. In the summer days due to the higher sun position, sunlight does not reach into the room and therefore allows the building to cool down. Figure 6 illustrates direct heating and cooling of a passive solar house. Inside air temperature can be reduced by absorbing heat from the air. This is commonly done with the use of the walls and floors. Deciduous trees can be planted on the northern and western face of the building to provide shade during the summer. Assuming the trees are properly watered, air passing through them will cool down before reaching the building [13].

Figure 6: Direct Heating and cooling [13]

Up to 53% of solar radiation is reflected back into space. Similarly the texture of a surface can reflect, transmit or absorb sunlight. This can be very useful when designing a building in different climate. A clear Glass permits up to 90% of radiation to pass straight through making it the fastest method of conduction in a dwelling. However walls with rough black surface tend to have lower U-values and absorb up to 95% of the radiation which makes it very efficient for heat storage. A smooth surface reflects up to 70% of radiation uniformly at an angle of incidence making it useful for hot climate where deflection of radiation is required. [13] Without a good glazing type, it can be nearly impossible to retain heat during winter seasons. Therefore it is vital to consider double or triple glazing when refurbishing a house or building a new project. Glazing is the glass part of a window which comes in different layers of glass with a thin gap of air in between enabling a better insulation. Glazing is commonly used in low temperature climate as its main purpose is to let as much light in while retaining heat inside a house. Typically a single-glazed window will have a U-value of 5.0 m²K, a double-glazed will have between 2.5 and 1.2 m²K and a triple-glazed will have between 1.0 to 0.6 m²K. Passive houses must be equipped with triple-glazed windows to achieve the regulations.

Figure 7: Direct Heating and cooling [13]

Thermal Mass

Storage of energy has always been the main challenge for a passive design [14]. One of the most efficient approaches of passive solar design is thermal storage walls which, as a form of indirect solar gain absorb solar radiation and release it slowly into a room. These walls are also called Trombe walls and are usually much thicker than ordinary walls, consisting of high density masonry. A Trombe wall is usually coated with black to increase the absorption. As described in Fig 8, the wall is covered by a layer of glass and heats up with solar radiation. During the day, warm air is trapped between the glass and the wall via radiation, and slowly travels through the higher channel into the room by convection, while cold air finds its path through the lower channel back in between the glass and the wall. This method is very successful but requires the wall to face south to absorb the required amount of solar radiation. At night the channel can be blocked to prevent any cold air from traveling in. This allows the wall to radiate its heat into the room.

Figure 8: Trombe Wall

The biggest issue about Trombe walls is the heat loss to the outside and in cold winter climate, triple glazing becomes necessary to improve the U-value. As described above, U-values determine the rate of heat exchange. Using equation 1, the total resistance (R-value) of a wall can be calculated by calculating the resistance of each individual layer (R1, R2 and R3) and adding them together. To calculate each R-value the thermal conductivity (k) and the thickness of the material must be known. The thermal conductivity of a material is the measure of how heat can travel through a material. Heat always travels from warm regions to cool regions in any type of materials as a result of temperature difference. The R-value is found by dividing k by L respectively for each material as shown in equation 2. The resistance can then help to derive the U-value demonstrated in equation 3 by obtaining the inverse and giving it units of W/ m²K.

The efficiency of the thermal mass can be calculated by analysing the absorbed heat qabs and the emitted qem. The Trombe wall is subjected to solar radiation and depending on the seasonal climate, the intensity of the radiation, and the surface area of the Trombe wall, a change in heat exchange can be recorded. Equation 1 calculates the heat exchange in the Trombe wall via radiation. The equation can then be separated into 4 equations to calculate q_abs and q_em (See equation 5 and 6 respectively). q is the heat loss, A is the surface area, ε is the emitted heat, α is the solar irradiation, Ϭ is the stefan - Boltzmann constant, T_s is the surface temperature of the wall and T_sur is the surrounding temperature.

In terms of comfort the best wall thickness is 0.61 m as it provides lower variation of temperature on the inside surface. However in order to reach highest temperature in a room, the best thickness of a wall lies between 0.23 and 0.4 m as it conducts heat a lot quicker. This can be an issue as colder temperature can be transmitted quickly through thinner walls and therefore cause the temperature to fluctuate throughout the day. Below, Figure 9 describes the variation of inner face of walls with thicknesses 0.15 m and 0.61 m. [14] Trombe walls can sometimes be constructed with a sunspace, where a room is attached to an existing south-facing wall of a building. The advantage of a sunspace is that during good solar days, excess heat collected can be circulated into the house with the use of Trombe walls and floors. It is said that the rule is to use 0.04 to 0.09 m2 of rock storage for each square meter of south-facing windows [14]. A sunspace is mainly constructed of glazing and can collect a great amount of heat.

Figure 9: Temperature difference between 0.15m and 0.61m Thick walls during a 7 days period

Under-floor Heating (Active System)

Under-floor heating (or also known as radiant heating system) has two types of systems on the market. The first one being an electric heating system has current flowing through a conductive heating material which allows the floor to heat up. Generally an electric system can heat up a surface within 30 to 60 minutes. Thermostats are installed to operate the perfect temperature for the room. The second type of heating is a hydronic system. It utilises fluid to heat up or cool down a surface. A hydronic system requires the installation of a boiler which transfers the heated fluid in a closed loop under the floor. The boiler can then be heated by natural gas, coal, oil or electricity (solar power) which is an advantage as the owner can decide which way is the most convenient.

Figure 10: B.E.R. Rating Values in kWh/M² [21]

240,833 dwellings have been assessed until September 2011 and of which 7250 have been certified. The average rating in Ireland for new and existing dwellings is listed below. All information was obtained by the Sustainable Energy Authority of Ireland (SEAI) [22].

For existing domestic dwellings, the average lies around a rating of C3 which gives a consumption of less than 150 kWh/m² per year. This shows that despite innovation such as insulation and airtightness, the average rating is far from reaching an A. For new domestic dwellings, the estimated average is between a B2 and B3 ratings which indicates a consumption of less than 75 kWh/m² per year. This was calculated from a population of 26,433 dwellings.

An extensive improvement will need to be made for Irish dwellings to match similar criteria of 15 kWh/m² per year of the PassivHaus standard. The statistics proved that existing dwellings in Ireland can save over 100 kWh/m² per year if the PassivHaus standard was matched, while newly built dwellings could save up to 60 kWh/m² a year.

Figure 11: Comparision of B.E.R. Distribution betweem Existing and New Dwellings

Costs vs. Savings

A passive house generally costs 5 to 20 per cent more than a standard home due to the superior insulation [23]. However according to the International Passive House Association, regardless of the regional climate a newly built passive house should benefit from consuming 80% less on heating and cooling than a conventional building. This is a result of strong specific standards which have been set up regulating the passive solar dwelling market. The certification requirements for passive houses state that heating load must not exceed 10 kWh/ m², while the energy demands for the total amount of domestic hot water, heating, cooling and auxiliary electricity must not exceed 120 kWh/ m². [16]

To ensure a design can meet the required specification, there are calculations which can be operated prior to construction. There are some software packages and passive house consultancies who offer calculations for their clients in wish of restoring their dwelling or building a new one.

The Passive House Planning Design Package (PHPP) is most used amongst engineers and architects in Europe. It is capable of calculating R or U-values of any elements in a design as well as the indoor air quality ventilation system, the heating domestic hot water system, auxiliary electricity and projections of carbon footprints CO2 emissions. This software takes the regional climate into consideration and can determine the perfect orientation for the house to harness maximum solar radiation. The design package has been rigorously tested throughout its development and was originally compared with average monitoring values of the first passive house made in Darmstadt, Germany (Figure 12). The data set on the left represent the average monitoring and on the right is the PHPP calculations. Each has the active solar and natural gas input verses heat loss. The comparison demonstrates that the PHPP package can obtain very accurate results. [24]

Figure 12: Comparison of average monitoring values vs. PHPP Calculation for Darmstadt Kranichstein from 1996 to 1997 [23]

Refurbishment vs. New dwelling

Ireland has a far superior CO2 emission compared to the United Kingdom and the rest of Europe. Although improvement has been seen in the domestic sector, Ireland is currently in a worst position than Europe were 20 years ago (see figure 13).

Ireland needs to incorporate passive solar design systems in dwellings and imply the passive house standard to maintain a similar standard to the rest of Europe. The do it yourself (DIY) approach has been very popular in the last few years as home owners just cannot afford to hire professionals to come in and restore their homes. Most current innovations are insulation, where either the interior or exterior of the house is re-enforced with latest insulating materials. Also double and triple glazed windows are usually a popular approach to solve high utility costs.

One of the most asked questions is whether a house should be refurbished in a manner to reach as many possible criteria for a passive house standard, or should a new project be started to support all possible technology required. The question is very difficult to answer as obviously it depends on the size of the investment, but it is clear that to reach a passive standard, the latter method is beneficial. In terms of emissions, construction of a new dwelling on average generates 50 tonnes of CO₂ where as a renovation of an existing dwelling would result to 15 tonnes of CO₂ [25]. Therefore the decision needs to be made carefully. In terms of passive house standard, a house cannot rely on passive solar systems for heating or cooling, and therefore requires a much higher investment to start with but pays off in later stage. Although some energy saving measures can be implemented at a later stage in a conventional building, it is often more expensive to retrofit and more than likely less effective [26]. As future dwelling criteria are leaning towards the passive house standard, it is advisable for home owners to consider building new dwellings complying with the future regulation.

Future Opportunities

The research has demonstrated that passive solar design has had an impact in the Irish market as new technologies have been invited into the economy. However it was realised after looking at the Irish climate that there is a definite need of strict regulations in order to turn every house into an energy efficient one. The energy consumption, especially for heating is too high and with better insulation and airtightness, Ireland can start battling against cold winters and a lack of sunlight caused by the cloud formation.

Below is a graph representing the energy usage per dwelling up to 2006 in Ireland, United Kingdom and the rest of Europe [26]. The energy was calculated by adding the electricity and the fossil fuel consumption in a year. It can be observed that Ireland in 2006 has still not cought up with the rest of the world while the United Kingdom are narrowing the gap. By implementing the right standard the energy consumption of Irish dwellings would slope downwards and match the 3 other curves.

Figure 13: Energy Usage per Dwellings Climate Corrected [26]

Ethical Considerations

There are ethical issues which may need to be considered when approaching the development of a project in the area of this document. Below are three main issue:

• Climate consideration: as described in section 1, every region in the world has a different amount of irradiation and engineers must be aware of any available methods to calculate the best location and orientation of dwellings to reach best possible efficiency.

• Education: the knowledge of available systems must be communicated to students in third level programs as well as employees in professional environment to enable an understanding of passive solar design and passive house standard.

• Installation of systems must meet international standard EN ISO 7730. This indicates the operations which result in reduction of heat loss and optimisation of thermal comfort.

Conclusion

• • The domestic sector accounts for 24% of the total energy demand in Ireland, only second after Transport. This is mainly caused by energy used for heating. By reducing the consumption of energy used for heating in a house, the total energy demand in Ireland can significantly reduce itself.

  • Ireland's irridation is mostly determined by its cloud formation. With cloud forming on top of Ireland for 50% of the time, only a low amount of irradiation can be gained. This should lead to carefulness and efficiency when absorbing heat.

  • Best possible system must be used in dwellings to maximise heat absorbtion.

  • Solar enegry must be stored appropriately to properly benefit from it.

  • Currently the passive house standard is the best in the market and has given exceptional results in the Europe and especially Germany. The standard must be applied in Ireland to improve the efficiency of dwellings.

  • When appropriate and possible, dwellings should be built from scratch to enable maximum efficiency as retrofitting cannot reach passive standard

• This will create green energy jobs for the future architects and engineers.

References

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