D20 Building guideline Slovenia in English - coolregion

7 steps
to energy efficient cooling
Guideline for investors and building users

Introduction
Energy Performance of Buildings Directive (91/2002/EC) (EPBD) promotes the improvement of
energy performance of buildings in the Member States through the implementation of ambitious
minimum requirements, not only for heating but also for cooling of buildings. Cooling of
buildings has in increasing impact on energy use. The main reasons are the climate change with
extreme summer temperatures and growing users’ demands about the living comfort.
Furthermore, cooling needs are increasing due to the architectural design which has in its quest
for freedom, forgotten traditional principles and materials for bioclimatic building design in hot
zones.
Energy efficient cooling of buildings comprises minimizing of cooling loads by good architectural
design, by the use of appropriate materials, by integrating passive cooling solutions and
efficient active cooling systems for covering of the remaining cooling demand, where the use of
renewables is strongly encouraged. These principles were first introduced in non-residential
sector, but recently they have found their way into residential sector as well. Despite
economical constraints imposed by investors on one hand, one can conclude that these holistic
solutions are a must for a low energy and zero energy buildings and for a high level of comfort
requested by demanding contemporary users.
This guideline presents basic principles for energy efficient cooling of residential and alike
buildings, presented in 7 steps.
Urbanism
Building and
microlocation
>>>
Building
envelope
>>>
Shading
Lighting
Appliances
Active
cooling
>>>
>>>
>>>
>>>
Figure 1. Cooling system is designed only after the implementation of cooling energy saving
potential due to good strategies in architectural design, selection of building components,
reducing internal heat sources.
1 Urbanism
The first step in design of sustainable thermal comfort in winter and summer period of the year
depends on the architect. When planning new areas the architect should note that the
agglomerated urban areas represent the heat island, where the local temperatures are a few
degrees higher than in their surroundings.
In the planning phase it is therefore necessary to avoid excessive heat mass in the vicinity of
buildings, foresee evaporating surfaces in the urban environment, use appropriate materials in
the design of urban areas that reflect heat rather than absorb it and last but not least plan a
sufficient amount of greenery and urban parks.
Urbanism has to be planned in a way that it allows air flows for cross ventilation of the city as
well as separation of districts with green zones.
1

2 Microlocation
What is relevant for energy efficiency in cooling periods, when planning microlocation of the
building The building concept as well as the user's profile can to minimize the cooling demand;
however the microlocation of the building plays also an important role.
When selecting the position of a building in the building plot, it is necessary to plan sufficient
vegetation around the building, as these results in a cooler air in the surroundings, better
chance of the ambient to be cooled by evaporation of the water in the vegetation and care of a
direct shading of facades. It makes sense to plan greenery in the form of green roof, as the
building is being additionally cooled by evaporation of water and on the other hand vegetation
prevents excessive absorption of solar radiation on the roof.
Water in the vicinity of a building cools surrounding air, so there are traditionally known
solutions with fountains, pools and water curtains. Bright areas around the building prevent
excessive heating of the surroundings. If the building is orientated with its main side (side with
windows) to south, as it makes shading easier and it is more consistent with the path of the
sun. Complex facade allows local wind turbulence and thus and additional cooling effect.
3 Building envelope
The building envelope with adequate thermal characteristics can significantly reduce heat load
from the environment. Heat storage capacity in the building envelope, shading of the
transparent part of the envelope as well as reflection of excessive solar radiation are significant
elements. Building physicists may prepare a detailed story for optimisation of heat flows in the
building and its envelope.
Heat storage capacity of a whole building and of its envelope should be designed. Thermal
mass within the building contributes to stabilised internal temperature, while the heat capacity
of envelope reduces the daily maximum temperatures and reassures the proper reduction of
temperature oscillation amplitude and guaranties the desirable time lag. In our climate it is
sufficient if the thermal insulation is placed on the outer side of the wall, so that the massive
walls play a role of heat storage. In the case of lightweight structures, only the floor structures
and partitions represent heat storage capacity. Heat storage surfaces areas should not be
covered with carpets and other coverings or with excessive amount of furniture. It is
recommendable to avoid double ceilings and double floors because additional layer hinders
accumulation of heat in the massive load bearing structures.
Thermal storage mass may also be planned as a part of a ground heat storage, rocks or water
heat storage or as a part of the system for cooling with activated concrete walls and roofs.
An advanced solution for the increase of heat storage capacity in the buildings with light
building envelope is to use phase-change materials (PCM), which melt at temperatures only
slightly higher than the temperature of thermal comfort and absorb a latent heat in the critical
periods of overheating of a building. Commonly used phase-change materials are encapsulated
or integrated directly in the gypsum matrix used for prefabricated boards.
The surfaces of the building envelope with a small albedo (white, reflective surface) ensure
small absorption of solar radiation on the external surface of a building envelope, which is very
important in the summer time. Good thermal insulation of a building envelope additionally
reduces conduction of heat from the exterior to the interior of the building.
Windows are the major reason of summer overheating, as solar radiation enters through the
glazing into a room and there converts into heat. It is important that the windows are equipped
with shading devices, most common are blinds (advanced blinds have separate control of the
lamellas in the area, which is intended for daylight source). West-oriented windows in the
sončno
sevanje
zračni tok
T i
konvekcija
infiltracija
zraka
T e
2

uilding envelope are not very desirable, as they contribute to a rapid rise of temperature in the
room. It is advisable to design a building in a way that working places are not exposed to high
direct solar radiation.
Good air tightness of a building envelope is necessary, as otherwise the cooling system
operates inefficiently, with high cold losses. Windows should allow opening, so that the benefits
of natural ventilation and night cooling of buildings can be used, whenever indoor air quality
requirements allow so.
4 Shading and daylight
Shading of building is one of the most important steps in design of summer thermal comfort in
the building. External system of shading is far more effective than systems with internal blinds
inside or with blinds between the glazing planes.
If architecturally acceptable overhangs and other immovable shading devices are to be used.
The combination of fixed and movable blinds is usually preferred. Modern glazing technologies
exhibit a wide range of optical properties, which are very important for optimized design of
cooling and dayligting. Advanced blinds allow separate control of the lamellas in the area, which
is intended for letting the daylight in the room.
Glazing with high reflectivity may be acceptable sun protection, if at the same time the
transmissivity for daylight is sufficiently high. Modern solutions of shading in low-energy
buildings are often combined with photovoltaic panels. A very interesting architectural solution
is the integration of transparent solar photovoltaic modules for shading, because in addition to
providing shading and electricity they also admit enough daylight.
The lighting design and sufficient covering of demand by daylight is important for the building
efficient efficiency, as the need for electricity used for lighting is then smaller. Daylight can also
be provided by lighting atriums or indirectly by reflection of daylight from neighbouring
buildings ether by prefabricated solar tubes.
The design of artificial lighting is a good opportunity to reduce the electrical power for lighting
by using energy efficient lamps. Sensors for the presence of people and the level of available
illumination by daylighting may reduce artificial lighting and thus contribute to energy savings.
5 Internal heat sources
Electrical devices use energy for their operation and represent additional internal heat load.
Various energy efficiency labels for appliances, which provide information about energy use of
devices in operation (www.greenlabelspurchase.net), are helpful in reducing the heat load
during critical periods of overheating in the building. An important issue in this field is the user's
attitude to rational use of energy; namely the appliances in a standby mode use energy in the
amount equivalent to the continuosly operating traditional light bulb; therefore it is reasonable
to use automated devices, which turn off all devices in standby mode.
6 Passive cooling
Building can be cooled by night ventilation, when air temperatures in the environment are
lower. The building fabric is thus cooled and as well as the diurnal room temperature gets
reduced for some degrees. Night ventilation can be natural or mechanical. Natural ventilation of
buildings can be supported by solar chimney, where the warm air, heated by the sun,
accelerates the natural convection of air through the building. An interaction of a solar chimney
3

very efficient in combination with a ground heat storage for preheating/cooling of air for
ventilation. In general, the use of ground water as a continuous source of cold is a very
economical source of cooling for passive and active cooling systems.
One of the bioclimatic cooling methods is also evaporative cooling (e.g. water curtains), known
in the hot dry areas.
7 Active cooling
In the Central and Southern Europe regions it is often impossible to fully satisfy the thermal
comfort requirements with previous six steps only. This is especially valid for commercial
buildings, where large heat gains appear due to people and devices. In such buildings
(especially the older ones without taking care for the relevant measures) a need for cooling is
often present for half of a year or even more. In the case, where we need cooling, it must be
carried out as the most effecient way, minimizing the use of secondary and primary energy. In
doing so, we meet with the contrast, since such systems have higher investment costs.
It is typical for cooling systems that the ratio between the energy consumption and nominal
cooling capacity power of devices is low. In residential buildings, this is due to the low number
of operating hours, and in commercial buildings, this is due to the relatively low cooling needs
during most of the cooling season.
Generally applicable measures and advices for the selection of individual cooling system don’t
exist, since we need to consider specifications of the building (the space for the installation of
devices and distribution of cold), as well as its location.
Elements of cooling system
The cooling sistem is composed of:
• Cooling device (chiller), which receives heat at a low temperature level and rejects it at
a higher temperature level, using additional energy (usually electrical),
• elements for distribution of cooled air or water throughout a building,
• cooling elements in rooms and
• heat rejection to the surroundings.
The cooling device
The cooling device for the building cooling is usually equipped with the mechanical vapor
compressor with evaporator, condenser and expansion valve. The trend of these devices is
increasing their compactness, which is also ecologically relevant, since the quantity of
refrigerant (usually a greenhouse gas) in them is small. It is also appropriate to use natural
refrigerant like ammonia (NH3), which provides high-efficiency of a cooling device, but we often
avoid it because of its toxicity and explosivty. New applications use a transcritical cooling
process with carbon dioxide (CO2) too. Refrigerant (CO2) is environmental friendly but the
temperature regime for building cooling does not allow high cooling efficiency resulted in higher
energy consumption.
Heat can also be used for cooling, when it represents driving energy for absorption chillers
(usually over 90°C). We take into account that absorption chillers have to reject more (about
35% for single stage) heat to the surrounding, than cooling devices with mechanical
compressors, using electrical energy. Lower driving energy temperature (~90°C) causes high
sensitivity on heat rejection temperature which should not exceed 35°C.
4

Advantage of solar energy used for cooling is that the largest heat gains and the highest
cooling requirements of buildings usually appear at the same time, during the peak of solar
radiation. Solar energy would be used as driving energy for absorption chillers, but it requires
huge solar collector area and is presently economically unacceptable. The solar energy for
cooling could also be used as driving energy for a sequence of drying adsorption or absorption
and humidifying of the air, where the sun regenerates ad(b)sorption media. In this case a
relatively large surface area for solar energy collection is also required.
The quality criterion of cooling device is the coefficient of performance (COP), which represents
the ratio between the useful cooling and input electrical power. Nominal COP does not present
the efficiency of the cooling system, because it is measured according to the conditions defined
in standards and guidelines. These conditions may take into account a partial load, which often
occur by cooling devices in buildings. Unfortunately it doesn't consider real temperature levels
and regulation. Due to changes in cooling load, it is appropriate to use more cooling devices in
cooling systems which allows the optimal efficiency of the device (the highest COP).
Appropriate regulation and settings have important roll in achieving optimal operation
conditions. It is recommended to decrease the frequency of start-ups as they cause damages
(shortens device life cycle) and reduces the overall efficiency of the system (losses).
Sufficient heat transfer area for coolant ensures that a cooling device operates at a higher
evaporation temperatures. This allows higher pressure and lowers pressure difference and ratio
between condensation and evaporation in the cooling device, which increases the efficiency of
the device (COP) and system as well.
9
8
7
6
35
45
55
65
COP
5
4
3
2
1
0
5 7.5 10 12.5 15
temperatura uparjanja [°C]
Figure 2. COP in dependence to temperature evaporation and condensation for R410A (Danfoss
Selection Software).
Heat rejection to environment
In most cases the heat from cooling system is rejected into the surrounding air - either directly
or indirectly. Direct heat rejection to the surrounding air lowers investment costs. Unfortunately
such systems are less energy efficient in particular in the case of higher external temperatures,
when cooling requirements of the buildings are higher.
Increasing the condensation temperature rises the condensation pressure which cause higher
pressure difference and pressure ratio and lowers efficiency. The system can be improved if we
spray water over condenser (indirect heat sink), but in this case chemical and biological
treatment of water have to be considered. Appropriate condenser design is required
(evaporative condensers).
5

When installing cooling device in the basement of buildings the distances to air condenser(s)
might be too long (pressure drop of refrigerant, gravity). In this case we have to use a coolant
(water or an aqueous solution) to distribute it to the cooler.
A more efficient system of heat sink is through cooling towers. The temperature of heat
rejection depends on wet bulb temperature, which is significantly lower than the air
temperature. Water takes the waste heat from the cooling device and rejects it through cooling
tower (different executions). Cooling system with cooling tower is more efficient than the direct
air-cooled condenser, although we have additional heat exchanger.
8
7
6
R134a
R407C
R410A
COP
5
4
3
2
1
0
30 40 50 60 70 80
temperatura kondenzacije [°C]
Figure 3. Effects of condensation temperature on COP at constant evaporation temperature
(5°C), (theoretical calculation).
It is also important to select the place for heat rejection. In addition to the manufacturer's
requirements for minimum distance from the objects it is favorable to avoid direct exposure to
the sun, or ground, which strongly warm up during summer. It is also important to prevent the
interaction between the elements of heat rejection.
Comfort in the rooms of commercial buildings and older residential buildings can not be
achieved without cooling. In most of these cases we need the active cooling. Due to the long
lifespan of buildings, the maintenance and replacement of cooling systems already is and will be
very important.
Our goal should be to reduce the need for cooling, especially the use of active cooling. Using
the passive cooling and renewable sources is desired where and when possible. With active
cooling, we have to pursue higher temperatures of cooling and lower temperatures of heat
rejection results in increasing efficiency and reducing energy consumption.
Cooling system will operate effectively only if all the elements are sized properly. Effective
cooling device alone does not guarantee high efficiency. If for example, the cooling elements in
rooms are undersized, a lower temperature of the coolant is required caused lower efficiency of
the system regardless the high quality of cooling device. For all the cooling systems,
irrespective of their size or mode of operation, it is considered to be more effective, if the
temperature differences between the temperature of the cooling (supply to the room) and
temperature of heat rejection is minimized.
The older air conditioning systems often throw away the air at the exhaust. Current regulations
require (reasonably) regeneration, because the biggest reduction could be achieved during
highest cooling requirements. In the design of new cooling systems and the reconstruction of
the existing ones we need to pay attention to the best use of an energy and the introduction of
renewable energy sources through the accumulation in the earth or solar energy.
6

7 steps to energy efficient cooling
Guideline for investors and building
users
EIE Coolregion – Energy efficient cooling in
regions of North and Central Europe
Agreement N°: EIE/06/026/SI2.439974,
Intelligent Energy Europe (IEE) programme,
Slovenian partner: Gradbeni inštitut ZRMK,
d.o.o
Authors:
dr. Marjana Šijanec Zavrl
dr. Janko Remec
Viri: www.coolregion.info
Gradbeni inštitut ZRMK, d.o.o.
Centre for indoor environment, building
physics and energy
Dimičeva 12
SI-1000 Ljubljana
Tel.: + 386 (0)1 280 84 01
Fax: + 386 (0)1 280 84 51
E - mail: info@gi-zrmk.si
Web: www.gi-zrmk.si
Information about best practice examples and
other guidelines for design of energy efficient
cooling of buildings is available at the website
of EIE project Coolregion
(www.coolregion.info).
The sole responsibility for the content of this publication lies with the authors. It does not represent the opinion of the
Community. The European Commission is not responsible for any use that may be of the information contained therein.
© Gradbeni inštitut ZRMK, d.o.o.
April 2009
7