Budownictwo o zoptymalizowanym potencjale energetycznym
2(10) 2012, s. 97-103
Stanislav TÓTH
Technical University of Košice
THE EFFECTS OF THERMAL STABILITY IN RESIDENTIAL
LOFT SPACES DURING SUMMER PERIODS
This paper aims to verify the procedure for calculated and measured values,
the effectiveness of varying insulation thicknesses for selected rooms and assessment of the highest allowable daily internal air temperature increases during
summer
periods. Residential building lofts are considered suitable, because in addition to
solving problems with sub-standard, common roof leaks, sloped roof constructions
significantly impact the architecture of the building and complement its overall
character.
Keywords: residential building lofts, summer period, thermal stability, thermal
comfort conditions, calculated and measured values
1. OVERVIEW OF CURRENT PROBLEMS
The design and realization of residential loft spaces in buildings and/or optimization of roof cladding construction design should adhere to relevant standards based
on the geographic location of the structure. The past decade witnessed the arrival of
many new building materials, construction technologies and procedures in dealing
with roof cladding. Roof cladding solutions differ from country to country and are
based on material inputs and production design, all of which depends on vernacular
traditions, raw material base and specific characteristics. An envelope/partition construction creates a defined boundary area between the interior and exterior or within
a building space. The room is characterized by a particular thermal environment,
which is dependent on the thermal state of the structure. An indoor space is regarded
as thermally stable when fluctuations in the internal state do not exceed standard
limits.
Thermal stability of the room for winter and summer periods is based on transient thermal conditions. Summer thermal comfort conditions are assumed to be
adequate for assessment purposes of residential buildings in terms of indoor thermal
stability:
θai + θs  51
(1)
S. Tóth
98
where:
θai - indoor air temperature [°C],
θs - average inner surface temperature [°C].
Table 1. Optimal parameters characterizing the thermal comfort of the indoor
environment for residential purposes during summer periods in accordance
with local regulations [2]
Building type
Maximum permissible
air temperature
θai,max [ºC]
Relative air
humidity
φi [%]
Minimum required
ventilation rate
vi [m/s]
Residential
25.5
35 to 50
0.1
Summer thermal stability of the room is assessed according to STN [1] and it, is
based on the maximal daily increase in room temperature Δθai,max , which satisfies
summer thermal stability conditions, when:
Δθai,max  Δθai,max,N
(2)
where:
θai,max - maximum permissible air temperature [K],
θai,max,N - maximum permitted daily indoor air temperature [K].
Table 2. The maximum permissible daily increase in internal air temperature during
summer periods in buildings not equipped with air conditioning systems [1]
Thermal Rating
Maximum permitted daily indoor
air temperature
Δθai,max,N [K]
A
5
B
7.3
2. SCOPE AND AIMS OF THE PAPER
The contribution focuses on thermal stability issues for loft spaces during summer periods and takes into consideration high ambient air temperatures and high levels of solar radiation. Summer climatic conditions dramatically increase the risk of
solar-radiation-induced overheating and are aggravated in loft spaces that use lightweight roof cladding.
The paper is based on theoretical analyses and test-measurements. It evaluates
the proportional influence of various alternating envelopes, cladding and internal
partitions for residential loft spaces suitable for transient summer thermal stability
The effects of thermal stability in residential loft spaces during summer periods
99
design parameters and aims to minimize energy consumption, which may occur during active cooling.
3. EVALUATION OF SUMMER THERMAL STABILITY IN SELECTED AREAS
Proposed alternative treatment procedures for loft envelope/cladding structures
include:
 Improving thermal performance by increasing the thickness of insulation - increasing the external thermal resistance of building structures.
 Modification of transparent structures - improved thermal insulation properties
of un-shaded windows with reduced solar transmittance.
 Increasing the heat-accumulating properties of boundary structures.
The paper involves the evaluation of thermal stability in proposed areas of
a double-storey apartment loft extension with a known cardinal orientation for
alternative envelope and transparent structure solutions.
In Figure 1 sections of transverse and longitudinal partitions and various internal
structures are circled within the test room. The present mezzanine level is
a multipurpose space and consists of an entrance hall, kitchen, living room and dining room with a spiral staircase that opens onto an upstairs gallery. South facing illumination of the room is realized using two double glazed wooden windows on the
first floor; South-East illumination is realized using floor - to - ceiling PVC framed
double glazing while the second floor loft is illuminated by Velux GGL skylights
which are orientated to the North.
Fig. 1. A transverse and longitudinal section of the test room
S. Tóth
100
Proportion of surface areas compared to the total area of the room (as a percentage)
is illustrated in Figure 2.
For purposes of the analysis, the compliance of desired adjustments required the
selection of the following roof systems:
 sloped roof cladding - lightweight design,
 envelope and gable - mass design.
Proportion of various construction areas as a function of total space area
93,0027
100
90
1,8408
0,64
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51,451
56,2583
80
Fig. 2. Graphical representation of the proportion of surface structures compared
to the total area of the test room
The first of these compositions is represented by 32.11% and the second by
12.78% of the overall surface area under consideration. Both compositions are
adapted in order to enhance thermal performance by increasing insulation thickness
as a method for improving the thermal stability of the room.
 By comparing the effect of altering insulation thicknesses, it can be deduced that
a 114% increase in thickness of the insulation failed to produce the desired reduction in the maximum increase in internal air temperature.
 Another alternative that compared the effect of changing exterior finishes also
failed to achieve a greater reduction in the maximum internal air temperature.
 By comparing the effect of altering transparent glazing structures, an initial
favourable reduction of maximum indoor air temperature was achieved, but
further improvements of glazing parameters failed to produce significant reductions.
 Comparing the impact of mass changes in the insulation layers by increasing the
weight of internal envelope structures achieved the greatest reduction in the maximum internal air temperature.
 Summer thermal stability was considered satisfactory for the test room once
modifications were carried out involving mass changes in envelope structures and
101
The effects of thermal stability in residential loft spaces during summer periods
changes in transparent glazing constructions; these achieved the greatest reduction in the maximum internal air temperature rise for the room in question.
Figure 3 compares the overall efficiency of structural variants for envelope claddings for summer thermal stability.
10,12 10,12 10,12
10,09
11
9,75
10,12
10,12
9,62 9,62
9,62
9,5
9,41
Maximum daily heat flow of indoor air (K)
10
9
8,06
7,65
7,8
7,33
7,34
7,37
8
9,34
9,28
7,27
9,23
7,03
7,3
7
6
5
7,3 K - Standard building norm for the
maximum permitted daily indoor air
temperature increase
Illustration of efficiency comparisons for varying space construction solutions according to thermal
stability during summer periods.
4
3
2
1
0
1 2 3 45
A
1 2
4
B
1
34 5
C
1
3
D
5
1
3
E
5
1
5
F
5
1
G
1
H
Alternative space construction solutions
1. The effect altering insulation thicknesses
3. The effect of altering transparent
5. The effect of density on modified indoor constructions
2. The effect of altering surface finishes
4. The effect of density on initial indoor constructions
Fig. 3. Graphical representation comparing the effectiveness of structural variants
of envelope claddings for the test room in terms of summer thermal stability:
1 - impact of changes as a result of variations in insulation thickness, 2 - impact
of changes due to external finish variations of vertical walls, 3 - impact of changes in
transparent glazing, 4 - the effect of mass regarding initial thermal insulation
thicknesses, 5 - the effect of weight adjusted for the thickness of the insulation and
changes
in transparent glazing structures
CONCLUSION
It is necessary to design pitched roof cladding as a whole from the outset - from
the inner to surface layers, including transparent roof structures with regards to indoor climatic conditions [3].
Significant influences affecting the thermal balance of loft spaces in summer include physical meteorological factors such as ambient temperature, solar radiation,
air flow and atmospheric precipitation [4].
High ambient temperatures, solar radiation, cladding with little accumulation
ability and poorly ventilated air layers will warm up an indoor space rapidly. Daily
fluctuations in indoor temperature will be higher, which adversely affects thermal
comfort for loft space occupants.
102
S. Tóth
The results of the test analyses regarding the effects of alternative solutions, envelope and related constructions for the production of summer thermal stability produced the following results:
 Increasing the thickness of the insulation above the threshold ensures the most efficient thermal insulation in winter, but has little effect in decreasing the highest
daily summer temperature increase of internal air. Similarly, increasing the insulations’ thickness may be considered negligible in relation to decreasing the maximum indoor temperature.
 Altering transparent glazing for greater energy-efficiency with reduced transmission of solar radiation can decrease the maximum daily-indoor-air-tempera-ture
increases several times more than increasing the insulation thickness of
lightweight pitched roof claddings.
 Replacing low thermal storage envelopes and complementing structures with
a material of high thermal storage capacity can achieve the greatest reduction
in the daily maximum indoor air temperature.
Excessive overheating in the summer can be avoided by:
 Determining the size and shading of roof windows depending on their orientation
and inclination.
 Increasing the thermal storage of envelope structures.
 Ensuring sufficient air exchange and ventilation.
 Increasing the thermal resistance of external building structures.
If these optimal envelope design requirements cannot be realized, it is necessary
for loft spaces to incorporate active cooling or air conditioning at the cost of increasing investment and operating costs to achieve thermal comfort [5].
Acknowledgements
The paper was realized through the project VEGA No. 1/1060/11 "Monitoring
changes in the physical parameters of envelope structures for buildings in quasistationary states undergoing dynamic changes in the external environment." The
aim of this project is to evaluate the latest findings and theories for civil engineering structures regarding building energy performance, as well as to verify implemented test structure measurements.
REFERENCES
[1] STN 73 0540 - Thermo-technical characteristics of building constructions. Parts 1-4, 2002.
[2] Chmúrny I., Thermal protection of buildings, Jaga group, Bratislava 2003.
[3] Oláh J., Characteristic defects of pitched roofs and their prevention. Roofs, Facades, Insulation,
Ostrava 2010, 2.
[4] Vyparina M., Tomko M., Tóth S., Durability and wear and tear of buildings in the expert practice, University of Žilina, 2008.
The effects of thermal stability in residential loft spaces during summer periods
STATECZNOŚĆ TERMICZNA W LOFTACH W OKRESIE LETNIM
Badania dotyczące stateczności cieplnej i warunków komfortu cieplnego ludzi
przeprowadzono w loftach. Opracowanie ma na celu zweryfikowanie wartości wybranych parametrów wyznaczonych na podstawie stosowanych procedur obliczeniowych i porównanie ic z wartościami zmierzonymi w warunkach rzeczywistych.
Oceniono efektywność różnych grubości izolacji dla wybranych pomieszczeń oraz
najwyższy dopuszczalny dzienny wzrost temperatury powietrza we wnętrzach w
okresie letnim. Lofty uznaje się za odpowiednie do kształtowania przestrzeni mieszkalnych, ponieważ pomimo problemów m.in. z niestandardową przestrzenią do zaaranżowania czy przeciekami dachów, nachylone konstrukcje dachowe wpływają
istotnie
na architekturę budynku i nadają jej niepowtarzalny charakter.
Słowa kluczowe: lofty, okres letni, stateczność cieplna, warunki komfortu cieplnego,
wartości teoretyczne i pomierzone
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