Category Archives: EuroSun2008-9

The potential for solar thermal heating and cooling systems to reduce. the carbon emissions of domestic properties in a northern European country

I. Knight1*, M. Rhodes1, F. Agyenim1 and E. Ampatzi1

1 Welsh School of Architecture, Cardiff University.
Corresponding Author, knight@,cf. ac. uk


This paper provides conclusions from a WERC-funded project undertaken to assess the potential for Solar Thermal Heating and Cooling Systems to reduce the carbon emissions from domestic properties in Wales, UK. The project is based on 4 main elements:

• the physical testing of a novel solar thermally driven air-conditioning system in the Welsh climate to ascertain the real-world and laboratory performances of the system as a whole and its principal components

• the characterisation of the Welsh Housing stock into 13 major construction types

• the thermal modelling of these 13 types to obtain their heating, cooling and DHW demands, and hence their ‘traditional’ carbon emissions and the ‘solar thermal’ carbon emissions

• the aesthetic and design issues to do with integrating such systems into domestic properties, and their potential effect on the overall system efficiency

This paper synthesises some of the findings from these elements to provide a first answer to the question about the potential contribution that Solar Thermal technologies could make to reducing the carbon emissions associated with heating, cooling and DHW use, from both new and existing housing in Wales. This paper presents these findings for each of the housing types individually, as well as for the domestic sector in Wales as a whole.

This information is of importance in establishing whether Solar Thermal should be part of the country’s future energy mix, and potentially how much it could contribute. The work is especially timely within Wales’ stated ambition for all new buildings to be built to zero carbon standards by 2011.

The main conclusion from this work is that the use of Solar Thermal for heating, cooling and DHW for domestic housing in Wales leads to predicted reductions between 10 — 25% in the total carbon emissions, regardless of the type or age of dwelling.

Keywords: Solar Thermal Cooling, Solar Thermal Heating, Carbon Emissions Savings, Existing Buildings, Solar Thermal DHW, Wales

1. Introduction

This paper presents the main findings from a physical and thermal modelling study of the potential for Solar Thermal Air Conditioning Systems (STACS) to reduce the carbon emissions from the domestic housing sector in Wales, United Kingdom. As an autonomous region of the United Kingdom, Wales is one of only 3 countries in the World which have a commitment to sustainability written into their constitution. It is now actively exploring how it might reduce its Carbon emissions as part of this remit. A Renewable Energy Route Map for Wales was published by the Welsh Assembly Government in 2008 [1] exploring how Renewable Energy systems might contribute towards this goal across all sectors of society.

Previous conference papers [2 — 4] have introduced the first findings from the project, looking at the operation of STACS systems and the Welsh Housing stock. This paper, along with other papers presented at the EUROSUN 2008 conference [5 — 7], complete the findings from this project to date.

This paper is in 3 sections:

• A short summary of the Welsh Housing stock showing the % of each type of house in Wales.

• A review of the modelling findings for the heating, cooling and DHW demands for each house type, with and without Thermal Energy Storage.

• A first assessment, based on the above sections, of the potential contribution that STACS might make to the annual heating, cooling and DHW demands in each type of housing, and hence the Carbon Emission reductions that might be achieved in the Welsh Housing sector as a whole.

Objective of the study

Single float glass transmits the majority of solar radiation between 315 and 2500 nm and absorbs other wavelengths. In real-time situations non-perpendicular incidence angles of radiation, double or triple glazing, additional low-E coatings, glass coloring and layer of dust and dirt on the surface result in much lower transmission of solar radiation than declared. When taking into account dirt on glass in a city environment (e. g. correction factor 0.8) and solar incidence angle typical of temperate climates (e. g. correction factor 0.8), transmission of single glass for visible light decreases from 89% to 57%

(89 % x 0.8 x 0.8 = 57 %). To decrease thermal transmission of windows, double or triple glazing is used. U value of a double glazing with air filling is usually about 3.00 W/m2K. If the window system is improved by a low-E coating with Argon filling, U value drops to 1.16 W/m2K. However, lower U value also causes lower transmittance for the visual part of solar spectrum (tv = 78 %) and lower transmittance for the whole solar spectrum (g = 63 %). Further improvements of U values bring us to the use of triple glazing (double low-E coating and Argon filling (U = 0.60 W/m2K) of Krypton filling (U = 0.58 W/m2K)). As mentioned above, further lowering of U values cause even lower transmittance for solar radiation.

Students also discussed the concept of passive house in relation to inside environment quality and compared the passive and the bioclimatic concepts. The goal of the passive house is the reduction of heating energy use to less than 15 kWh/m2a. To reach this goal, glazing — which interests us most — has to be triple. This consequently reduces the dynamic communication between the inside and the outside environment. In the philosophy of the passive house design the reduced daylighting and cutting off the direct contact with external environment is viewed as collateral damage. But the concept of alienating people from natural environment is according to many studies harmful. The external environment is not hostile; on the contrary, it has simulative effects on body and mind. Daylight provides quality lighting, stimulates the sense of sight and is an important communication between the internal and external space [3]. Constant changes of light improve concentration and responsiveness. The same goes for hearing and the sense of smell. The bioclimatic concept, on the other hand, is based on simultaneous adaptation to external conditions and internal needs. The closer the building is able to follow these two profiles (temperature dynamics, solar and thermal radiation, relative humidity and air stratification), the more efficient it is. The unstable model represents the dynamic structure, which functions in real time. The goal of the above-described interventions in the framework of bioclimatic design is a healthy living and working environment with low energy use and not low energy use with physiological minimum.

Glazing properties have direct influence on the level of daylight in living and working environment and on energy balance of buildings. Low daylight levels have proven negative influences on comfort, health and efficiency of people as well as on energy used for lighting and cooling of spaces. Studies

carried out in the 70-ies in the USA showed possible energy savings for lighting of office spaces in the range between 15% and 20% if enough daylight was available (also regarding quality factors) [3]. Lately the advantages and positive effects of daylight on efficiency and sales increase were proven in the HGM study [4, 5] carried out in 2003. Of course, lower U value of glazing decreases transmission losses through the building envelope, but when designing non-transparent parts with U values 0.2 W/m2K or lower, the majority of heat losses are produced due to ventilation, not because of heat transmission. Because of the above-mentioned reasons and complex influences on the functioning of the entire building system, window properties are not a trivial question and deserve a systematic analysis.


C. Silvi

Gruppo per la storia dell’energia solare (GSES) — Via Nemorense, 18 — 00199 Rome, Italy

E-mail: csilvi@gses. it


This poster presentation aims at introducing to the EuroSun 2008 participants the exhibition “Solar Cities From the Past to the Future: Scientific Discoveries and Technological Developments” opening in Rome in the spring of 2009. Now in its second edition, the first of which took place in 2006 at the Genoa Science Festival, the exhibition will be installed at two prestigious and symbolic venues, the Museum of Roman Civilization and the Central State Archive. In Genoa the message was: for thousands of years, and until just 200 years ago, human beings developed experience in building and operating cities run on solar energy alone. Can this experience be useful in designing the solar cities of the future? Is it possible to return to the use of the sun’s energy for lighting, heating and cooling buildings, for producing electricity, fuels, and construction materials for the cities of a technologically advanced world? The upcoming event in Rome will continue to explore these and other questions. Solar features of models of houses, baths, villas, preserved at The Museum of Roman Civilization, will be highlighted with the heliodon approach. The thesis that future or modern solar cities have their main roots essentially in the past will be reiterated.

1. Introduction

Renewable solar energy — what the sun sends us every day, the driving force of all forms of life on earth, of the winds and the water cycle, the growth of forests and other biomass — has always been, is and will always be the principal energy source on our planet.

All over the world, people used solar energy alone until barely 200 years ago, when fossil fuels — coal, oil and gas (actually fossilized forms of solar energy) — began to gain sway. Like nuclear fuel, these forms of energy are not renewable and eventually will be exhausted.

The use of renewable solar energy is thus an age-old experience marked by fundamental discoveries that made it possible to build cities that ran on solar energy alone, ranging from the discovery of fire, which enabled humans to use the solar energy stored in forest wood and other forms of biomass, to the discovery of agriculture and the birth of the first human settlements. The ancient Greeks’ discovery that streets and buildings can be oriented so as to exploit the sun’s light and heat directly and naturally gave birth to solar architecture. The Greeks’ idea was built upon by the Romans, as codified by Vitruvius in De Architectura, and handed down for centuries.

These discoveries characterize what I would call the primitive or ancient solar age. Though we take them for granted today, they are still of the greatest importance in our daily lives. It’s as if an ancient renewable-solar-energy soul were living on in the cities of our modern world, nearly forgotten and not accounted for

If our forbearers were able to build and run cities with renewable solar energy alone for thousands of years, is it not possible for us to do so in the future? This question was raised explicitly in the 1st edition of the exhibition “Solar Cities From the Past to the Future: Scientific Discoveries and Technological Developments” promoted and organized by the Italian Group for the History of Solar Energy (GSES), and the “Italian National Committee ‘The History of Solar Energy’” (CONASES), a multi disciplinary non profit entity established in 2006 by the Italian Ministry for Cultural Heritage and Activities. The exhibition was held during the Genoa Science Festival at the Doria Pamphilj Prince’s Palace from October 26 to November 7, 2006 [2][3].

Подпись: Fig. 1 . Map of Imperial Rome, showing locations of the major baths, facing south or southwest (From a Golden Thread, by K. Butti and J. Perlin, 1981) Подпись: Fig. 2 . An aerial view of Spello, a typical Italian small town, whose shape and relationship with the surrounding farmland is a reminder of its solar past (Foto G. Reveane, 1993).

The exhibition traced the evolution of the Italian human habitat from antiquity to the present day and with a look to the future. It recounted the changes in cities, architecture and energy and food — supply infrastructure, and the scientific discoveries and technological developments that marked the major stages in their history, for instance the Romans’ introduction of flat window glass 2000 years ago [1].

Visitors to the exhibition at the Prince’s Palace were able to explore solar city past, present and future with the aid of more than 40 posters, various videos, seminars and conferences. A brief video report of the exhibition is available on You Tube [4].

A city of modern or future solar age has its roots in the discoveries and inventions made during the Renaissance and the scientific revolution. One example of the progress made over the past five hundred years is the giant steps taken in the understanding how light works by great scientists such as Galileo, Leonardo, Newton, Huygens, Maxwell, Planck and Einstein. The explanation of the photoelectric effect by Einstein contributed to underscore other aspects of the structure of the atom, the nature of light and the electrical origin of the cohesive forces in molecules and matter. All this has opened fascinating prospects for the use of direct solar energy in the modern or future solar age, from solar cells with efficiency ratings of 50% or more to smart glass and photon solar architecture and city planning.

Will scientific discoveries and technological developments allow us to build the solar city of the future, a city powered solely by solar energy?

A thesis presented in Genoa by GSES and CONASES was that to bring the modem solar city into being we must intelligently combine and integrate the experience gained by the ancient cities — not only in terms of technical know-how, but also of art, culture, relations and communication — with the many solutions made available by the scientific discoveries and extraordinary technological developments of the past two hundred years, especially the most recent decades. In other words, as suggested by Norbert Lechner, “Use the best of the old and the best of the new.” [5]. This thesis will be reiterated in Rome’s exhibition.

The impact of water heating on the overall consumption of electric energy in Brazil

Based on the results from the latest survey, it is estimated that 22.6% of the electric energy consumption of the residential sector is using an electric shower device (Figure 1) which instantaneously heats the water as it flows through it commonly called Instantaneous Electric Shower Device; in turn, this represents about 6% [7] of the electric energy consumption in the whole of Brazil (± 22 TWh).

The graph of the average residential load curve in Figure 2 reveals that it is at peak-hour_ normally between 06:00PM and 09:00PM_ that the use of electric shower as a water heating device is the most widely spread [1].

The value indicated in brackets in the key corresponds to the percentage in electric energy consumption for each domestic piece of equipment.

image002 Подпись: □ Microwaves (0,1%) □ Washing machine (0,4%) □ Iron (2,6%) □ Sound (3,5%) □ TV (9,5%) □ Air conditioner (19,8%) U Electric shower (22,6%) □ Rumination (14,3%) □ Freezer (5,2%) □ Refrigerator (22,1%) image004

The load curve of the Brazilian Electrical System-BES, on a typical day, is shown in Figure 3 [11]. Fig. 2. Residential Average Load Curve (W) Fig. 3. Load Curve of the BES (MW)

These studies about the Ownership and the Utilization of Equipments (Pesquisa de Posse de Equipamentos e Habitos de Uso — PPH in Portuguese) coordinated by PROCEL/Eletrobras, are also meant at qualifying the type of ownership, using a customised questionary but with the same standards of measurement from other research institutes for relevant comparison. Through the careful analysis of the individual answers from end consumers regarding the use of their domestic equipments, it is possible to raise important data about living conditions and socio-economic information for example, as well as about the quality of the electric energy supply as a whole, market changes following the electric energy rationing of 2001, domestic appliances purchasing habits etc.

Table 1 shows a summary of the comparative data from the various surveys ran by PROCEL between 1988 and 2005 about instantaneous electric shower ownership in Brazil: it is clear that the number of households using this device increased over those 17 years.

Table 1. Percentage (%) of Brazilian households with electric shower





















In 2005, 42 % of all residencial electric showers were turned on between 06:00PM and 07:00PM causing the Brazilian Electrical System-BES to reach its maximum level in electric energy demand.

There was also a noticeable change of habits in the first hours of the day. Whilst in 1988, 10% of all households in the country had at least one person using this equipment between 06:00AM and 08:00AM, in 2005 this percentage had increased to 31%. (Figure 4).

Fig. 4. Use of electric shower (typical day)


According to Table 2, the Southern region not only has the highest index in electric shower use as well as the highest average ownership with 1.17 electric shower per household_ way above the national average of 0.89.

Table 2. Average ownership of electric shower per household in unit (2005)













Futhermore, it appears that 21% of all interviewees, by 2005, had already switched electric shower devices for solar heating systems. A new demand is also emerging by means of the efforts of a few Brazilian municipalitiescouncils to integrate within their City Planning Directives the obligation, for all new buildings, to offer solar collectors installation facilities.


PROCEL has been focusing, with partner entities and enterprises, on promoting the technological development of equipments using solar energy for water heating.

The Welsh Housing stock

Error! Reference source not found. shows the main dwelling types in Wales and the percentage of the total housing stock that each type occupies. It can be seen that the semi-detached house is by far the most common residential property type, accounting for 44% of the total housing stock, excluding year 2000 onwards properties. The data in bold type shows the building types modelled in this project. These models can be seen to represent around 50% of the total housing stock. A suitable Case Study of a pre-1919 terrace could not be found, but if we were to model this as well then 66% of the housing stock type would be covered.

No data for post-2000 dwellings

Подпись:Rhodes et al [3] provides greater detail of the housing stock, including physical properties, improvements, etc., but it is clear that a large percentage of the housing stock was built before energy efficiency was a serious consideration.

From figure 1, taken from the Renewable Energy Route Map for Wales [1], we see that the domestic sector accounted for 23% of the total carbon emissions in Wales in 2003. The breakdown between electrical and thermal demand is not known.

For this paper the annual electrical demand for each of the dwellings is taken to be 3090 kWh [8].