Patrycja Kochaniuk
Passive solar design
Patrycja Kochaniuk, January 2012
Adapted from: ‘To what extent can passive solar design strategies influence energy savings in a Passive House
refurbishment of a typical 1960’s semi-detached Dublin house?’ Graduate School of the Environment, Centre
for Alternative Technology, MSc Architecture: AEES
Passive solar design
1. Introduction
This essay examines possible passive solar design strategies for a refurbishment of a typical 1960’s
semi-detached house in Dublin and evaluate their influence on energy savings. It focuses on
strategies applicable to refurbishment of an example house and quantify possible gains of solar heat.
It is acknowledged in Ireland that the poor energy and CO2 performance of the existing housing stock
needs to be addressed (Department of Communications, Energy and Natural Resources, 2009). One
of the measures helping to improve energy efficiency is the engagement of the passive solar
strategies. I will show which solar techniques are feasible in a refurbishment of an existing house and
what heat gains can they provide.
First, the general principles of the passive solar design are introduced. In order to explain how they
can be adapted to the example house, the case study house is introduced. Finally, the upgrade
options for maximizing winter solar gains and the techniques for minimising the summer solar gains
are presented.
2. Principles of passive solar design
In passive solar design the building elements (windows, walls and floors) can be used to collect, store
and distribute solar energy in the form of heat in the winter and reject solar heat in summer (Fig. 1)
Windows are acting as collectors – they let the radiation in the house. The heat is then absorbed by
suitable surfaces (for example dark floor tiles) and stored in the thermally massive building elements.
Finally, the heat is transferred from the warm surfaces by radiation and then passed to other parts of
the building by air convection currents through open doors or high level vents between the rooms.
Harris and Borer (2005) claim that houses with warm air central heating or whole house ventilation
tend to achieve better distribution of solar heat.
The main strategies listed by Randle (2008) for maximizing winter solar gains are direct gain, isolated
gain systems and indirect gain. The indirect gain is provided by a masonry wall located behind the
glazing and its thermal mass acts as absorber, store and heat emitter. Such approach usually
requires the whole elevation to be glazed which would be inappropriate for the urban semi detached house retrofit. Thus, only direct gain and isolated gain systems are considered to be useful
for the retrofit situation.
Both those systems rely on large glazing for increasing solar gains in winter. It is important however
to minimise summer solar gains as they may cause overheating. The southern orientation of solar
windows is especially effective with that regard as the sunlight would reflect off the window glass
when the angle on that side is steep in summer. Fixed shades, like roof overhangs are most useful on
the south, as well as they can be designed to maximize the gains in winter and block direct light in
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summer. Another way of minimizing the impact of summer overheating is the use external or
internal vertical shading elements and a natural cross ventilation strategy.
Fig. 1 - Five elements of direct gain design: Aperture (Collector), Absorber, Thermal mass, Distribution
and Control. Source: EREC (2001)
3. Adapting the passive solar strategies for the specific retrofit situation
A. A base for the case study
The case study example is a typical semi-detached 1960’s Dublin house. Originally, the entrance hall
and a living room were positioned at the front (east-south orientation) and a dining room and
kitchen at the back of the house. Luckily for this example, the living room has a reasonably large
window to south-east (as other houses on that street would have the same layout with varying
orientation). All the rooms are separated by partition walls. The position of windows and doors does
not provide visual connection or access to the garden. The original structure of the house comprised
of uninsulated concrete block walls, suspended timber floor and no insulation in the roof area.
Windows were single glazed.
As it is crucial to minimise all heat losses before implementing solar energy design (Kwok and
Grondzik, 2011), the house was first virtually upgraded. It was decided to use the Passive House
guidelines (Feist at al, 2007) with that regard as they provide a clear set of rules for achieving a good
level of energy efficiency and the standard was verified by a number of applications in Europe
(Schnieders, J. , Hermelink, A. , 2004). The base house drawings and solutions for fabric insulation,
airtightness, ventilation and heating systems are all explained in Appendix A. They take into account
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the restrictions of the retrofit situation, such as the influence of unavoidable thermal bridges and the
building’s elements dimensions. The house’s energy performance was modelled in the PHPP (Passive
House Planning Package 2007), software developed by the Passive House Institute for verification of
the building’s energy efficiency.
The base of the case study is then an existing house, upgraded with energy efficient measures
described above, but with the original layout, including window sizes and orientation.
B. Direct gain
Direct gain is the simplest form of passive strategy. Solar energy enters through glazing and warms
up a wall or a floor which will absorb, store and emit the heat. In the northern hemisphere the most
of solar energy is received on a south face (with small differences within 25 deg. off due south), so
the design will require large south-facing windows. The optimum size depends on its thermal
performance and solar transmittance and can be optimized using PHPP software. Excessive heat
losses at night can be prevented by the use of high performance glazing and installing thermal blinds
or heavy curtains. Internal layout should reflect the location of the biggest windows – main living
areas should be laid out on the south side. Windows to the north should be the smallest possible for
the daylight requirement (10%- 15% of the floor area) and that side of the house should be reserved
for not habitable rooms such as stores, utility rooms, etc.
Implementing direct gain principles in the case study house (design option 1 – Appendix B) included
enlarging of the front window openings from 20% to 44.2% of the front wall area. It was the
maximum feasible change taking into account the internal layout and building regulations
restrictions. The area of north-east and north-west windows was reduced from 24.7 % to 17.5%, and
their revised design is also providing better access to the garden. There are two internal layout
options for the same windows arrangement presented in Appendix B. In option 1A most of internal
partition walls on ground floor were removed to allow for free flow of light and more even
distribution of solar heat. Option 1B proposes more changes. The staircase moved to the other side
of the house ensures better access to the side garden and helps to enlarge the small front bedroom
to make a better use from the heat gains. Drawings showing options 1A and 1B and windows areas
can be found in Appendix B. All those changes resulted in an increase in the solar gains of
12kWh/m2/year, as calculated in PHPP and reduced a requirement for space heating from
22kWh/m2/year to 15kWh/m2/year, an improvement of 32%.
The area of thermal mass required to store the solar heat can be estimated by a general rule. The
heavy mass elements of a thickness of about 100-150mm that receive direct irradiation should be
about three times the area of the solar glazing (Kwok and Grondzik, 2011). It needs to be twice as
much for elements with reflected radiation. In the example house the south-east solar collecting
widows are 15.6m2, so there would be a need of 47m2 of directly irradiated heavy thermal mass.
About 32m2 is available on the ground floor for direct radiation (concrete floor). It would leave 15m2
x 2 that could be covered by reflected radiation. There is 30m2 of the dense concrete external or
party walls on ground floor and additional 20m2 on first floor which would cover the requirement
(the thermal massive elements are marked on the Option1A drawings in Appendix B). To help with
heat absorption, the ground floor is dense concrete with a dark-coloured clay tiled surface.
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C. Isolated gain
Isolated gain systems, e.g. conservatories, are glazed spaces that can be opened to the house to
allow circulating collected heat inside, but can be closed off at night. Thus it is important that they
are thermally separated from the house. Conservatory works both as a tool for direct gains, but also
plays a role of a buffer. The air within the conservatory will always be warmer than outside, so
windows and walls facing the conservatory will lose less heat. The orientation of conservatory is not
as critical as for other direct solar openings.
In the case study house a conservatory could be added as an isolated gain system (design option 2 –
Appendix C). It was designed at the back of the house, as it would be a position most desired by the
occupants. It means its glazing is exposed to north-west and north-east. It is not the most desirable
orientation, but would still provide some heat gains in the morning and in the evening, and at the
same time would not be susceptible to overheating. It was estimated that the possible heat gains
would amount to 715kWh/year from the north-west glazing and 224kWh/year from north-east one,
which adds up to 10.20kWh/m2/year. Of course it would be difficult to distribute all that heat gains
throughout the house; but even if 30% could be transferred, it would decrease the space heating
requirement from 15kWh/m2/year to 12kWh/m2/year, providing improvement of 20%. Other
benefits include attractive additional living space and a benefit of a temperature buffer at the garden
door.
D. Shading
The procedure of establishing the most appropriate width of the fixed overhang to maximize the
gains in winter and block direct light in summer is described in Fig.2.
OVERHANG SIZING RULES:
1. Draw the wall to be shaded to
scale.
2. Draw the summer sun angle (in
Dublin 63 deg.) upward from
the bottom of the glazing.
3. Draw the overhang until it
intersects the summer sun
angle line.
4. Draw the line at the winter sun
angle (in Dublin 16 deg.) from
the bottom edge of the
overhang to the wall.
5. Use a solid wall above the line
where the winter sun hits. The
portion of the wall below that
line should be glazed.
Fig. 2 – Overhang sizing rules. Adapted from: EREC (2000)
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Moveable external shutters would be more effective than internal, but not used at all in Ireland (they
are popular in Mediterranean countries). Internal shading absorbs the radiation that has already
come through the glass and most of it would remain within the space. Nevertheless, venetian blinds
are useful for an issue of overlooking as they give control of the extent of the shading and can also
scatter the sun’s incoming rays – distributing the heat over a wider surface.
Natural cross-ventilation strategy relies on opening windows during the night, when the
temperature outside is lower than inside to cool the house. It is especially important in case of
conservatories and sunspaces to allow for low and high operable glazing sections and manually
operated shading for glazed roofs. The air exchange is initiated either by wind or by temperaturecaused differences in density. If internal doors can stay open at night, the use of the chimney effect
spanning two storeys is particularly effective and can be driven by two windows (on ground and first
floor) manually opened during night (Feist at al, 2007)
Mlakar and Strancar (2011) investigated the summer overheating issue in a passive house located in
northern Slovenia. They concluded that it is possible to keep the summer temperature within a
comfortable zone using southern windows horizontal overhangs, manually operated external
shutters for east and west windows and by night ventilation. A comparison of the simulated results
with measured values proved that it is very important that the residents are instructed and willing to
rigorously adopt the strategies to maintain comfortable environment. With the milder climate in
Ireland, achieving appropriate indoor temperatures is easier than in Slovenia. Calculations for the
example house showed that one set of operable windows sections (ground and first floor) provides
enough cross-ventilation to keep the indoor temperature below 25 degrees in summer.
4. Conclusion
To summarize, the essay presented passive solar design principles suitable for the specific case study
house. It was established that their influence on the energy efficiency of the house is substantial.
Implementation of the presented direct solar gains measures decreases the space heating
requirements by 32% and a conservatory could contribute further 20% improvement.
The orthodoxy with regards to the typical 1960’s estate houses design (such as the example house)
was a complete lack of regard to passive solar gain principles. Currently, even though the use of solar
techniques still cannot be observed with relation to Irish mainstream estate design, there are some
examples of individually designed houses that fully utilise solar energy, for example the Passive
House certified dwellings. When it comes to refurbishment projects, the solar design implementation
is more restricted by existing conditions and would be guided by the project’s budget. As it was
shown that passive solar techniques can bring substantial heat gains, it can be concluded that they
are worth pursuing whenever possible. It was also proved that the gains can be verified. It is worth
mentioning that beside the heat gains benefits, orienting the house with reference to the sun
position could also bring savings in energy spend on lighting and improve indoor environment.
This essay is limited by the fact that it focuses on one specific example and does not extend the
findings to wider applications. It would be beneficial to find out if proposed solutions bring similar
gains in different house types and orientations. Also, the cost implications of direct and isolated gain
elements were not verified in the case study so it is difficult to say if they are justified economically
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5. References
Ireland. Department of Communications, Energy and Natural Resources (2009). Maximising Ireland’s
Energy Efficiency. The National Energy Efficiency Action Plan 2009-2020. [Online] Available at:
http://www.dcenr.gov.ie/NR/rdonlyres/FC3D76AF-7FF1-483F-81CD52DCB0C73097/0/
NEEAP_full_launch_report.pdf (Accessed: 24 February 2012).
EREC (2000) Technology Factsheet: Passive Solar Design. [Online] Available at:
http://www.nrel.gov/docs/fy01osti/29236.pdf (Accessed 13/03/2012) EREC - Energy Efficiency and
Renewable Energy Clearinghouse.
EREC (2001) Passive Solar Design for the Home. [Online] Available at: http://www.nrel.gov/docs/
fy01osti/29236.pdf (Accessed 13/03/2012)
Feist, W., Pfluger, R., Kaufmann, B., Schnieders, J. and Kah, O. (2007) Passive House Planning Package
2007. Requirements for Quality Aprroved Passive House (2007). [Computer program]. Passivehaus
Institut. Darmstadt.
Harris, C. and Borer, P. (2005) The whole house book. 2nd ed., Aberystwyth: Centre for Alternative
Technology.
Kwok, A. and Grondzik, W. (2011) The Green studio handbook, environmental strategies for
schematic design. 2nd ed., USA: Elsevier.
Mlakar, J. and Strancar, J. (2011) ‘Overheating in residential passive house: Solution strategies
revealed and confirmed through data analysis and simulations’ Energy and Buildings. 43 (2011), pp.
1443-1451.
Randle, D. (2008) Passive Solar Design Strategies. CEM 161, MSc Architecture: Advanced
Environmental and Energy Studies by Distance Learning, Graduate School of the Environment, Centre
of Alternative Technology, Machynlleth.
Schnieders, J. and Hermelink, A. (2004)’ CEPHEUS results: measurements and occupants’ satisfaction
provide evidence for Passive Houses being an option for sustainable building’ Energy Policy. 34
(2006), pp. 151–171.
6. Appendices
Appendix A:
 Existing house drawings(1:100)
 Retrofit specification
Appendix B:
 Option 1A drawings – revised windows (1:100)
 Option 1B drawings – revised windows (1:100)
 Revised window sizes
Appendix C:

Option 2 drawings – conservatory (1:100)
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APPENDIX A
Retrofit specification
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APPENDIX B
Revised window sizes (the same for Options 1A and 1B)
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