Passive Heating Systems: A Case Study in a Brazilian ... · bioclimatic building design. His method was based on a “bioclimatic chart” showing the human comfort zone in relation

Journal of Civil Engineering and Architecture 13 (2019) 676-685 doi: 10.17265/1934-7359/2019.11.002

Passive Heating Systems: A Case Study in a Brazilian Mountainous Region

Ana Clara L. Pereira1, Ana Lúcia T. S. da Motta1, Bruno B. F. da Costa2, Priscilla C. P. F. de Oliveira1 and

Thiago V. Miranda1

1. Programa de Pós-graduação em Engenharia Civil, Universidade Federal Fluminense, Rio de Janeiro 22211-200, Brazil

2. Departamento de Engenharia Civil da Universidade Federal do Rio de Janeiro—Campus Macaé, Rio de Janeiro 22211-200,

Brazil

Abstract: The study of thermal comfort in the built environment is of great relevance since it stimulates the development of more sustainable buildings suited to the local climate and able to meet the human need for well-being. The objective of this research was to develop, construct and test a passive heating system adaptable to existing buildings, reducing the need for major interventions and increasing thermal comfort in the indoor environment. The adopted methodological approach was a case study in a single-family residence located in the Brazilian city of Petrópolis, a mountainous region with a humid subtropical climate and a rigorous winter. The proposed passive heating system is totally isolated, thus mitigating air infiltration and promoting increase of temperature in the internal environment through the absorption of solar energy and greenhouse effect. This kind of solution is especially interesting for residents of this region, since most of the city buildings are not adequately prepared to handle low temperatures. Thus, given local climatic conditions, residents need to spend a lot of money on the acquisition and operation of electric or gas heating systems. The results indicated that the developed system, in fact, increased the temperature of the studied room when compared to an adjacent room, which did not receive the device. The findings of this paper, therefore, provide a valuable reference for experts and practitioners in the selection of heating systems to be used in cold regions, and proved that passive systems can provide thermal comfort at the same time that optimize the interaction of the building with the local ecosystem.

Key words: Passive heating systems, thermal comfort, bioclimatic architecture, sustainable buildings.

1. Introduction

Over the last decades several studies have focused

on developing, during the early building design stage,

a systematic approach adapted to human requirements

and prevailing climatic conditions. Attempts have

been made to define the appropriate building design

strategies for a given region according to their climate

and specific needs [1]. Olgyay [2], in the 1960s, was

the first to propose this systematic approach of

bioclimatic building design. His method was based on

a “bioclimatic chart” showing the human comfort

zone in relation to the dry bulb temperature (vertical

axis) and relative humidity (horizontal axis). The

effects of mean radiant temperature, wind speed and

Corresponding author: Ana Clara L. Pereira, M.Sc.,

research field: civil engineering.

solar radiation were also considered. Afterwards,

bioclimatic charts based on typical psychrometric

charts were developed by Givoni [3]. More recent

works included the control potential zones and the

graphical design tool involving comfort triangle charts

[1].

According to Ref. [4], thermal comfort can be

defined as the “condition of mind which expresses

satisfaction with the thermal environment”.

Furthermore, user’s thermal comfort sensation is a

cognitive process which depends on several

circumstances apart from the air temperature.

However, even though climates and cultures differ

around the world, the indoor air temperature selected

by people under the same conditions (relative

humidity, air velocity, physical activity, among others)

is very similar [5]. Cañas and Martín [6] reported that

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Passive Heating Systems: A Case Study in a Brazilian Mountainous Region 677

“during hundreds of years man has developed some

constructive techniques to obtain the internal comfort

considering the local climatic conditions, the available

materials and other conditions relating to culture”.

The result of this global effort was the creation of a

sustainable (or bioclimatic) architecture concept,

which refers to an alternative method of construction

in which passive technologies are utilized with the

aim of improving energy efficiency based on the use

of the local climate conditions [7].

The bioclimatic design benefits from the climate to

bring its occupants as close to the comfort conditions

as possible. It is necessary to use several strategies

adapted according to the season, disposition of

buildings (orientation related to the sun and wind,

aspect ratio), space (site planning), air movement,

openings (size-position, protection) and the building

envelope (walls, construction material-thickness, roof

construction detailing) [8]. In summer, for example, it

is necessary to cool the building using intensive

ventilation (cooling strategy). On the other hand, in

winter, it is important to benefit from the solar

contributions and to be protected from the cold

(heating strategy).

The objective of this research was to develop,

construct and test a passive heating system in a

residence located in the Brazilian city of Petrópolis, a

mountainous region with a humid subtropical climate

and a rigorous winter. Considering the limited

quantitative studies available for the Brazilian climatic

conditions, this approach becomes extremely relevant

in order to highlight the importance of the bioclimatic

design. The proposed objective was achieved with the

installation of a prototype system in a room of the

residence studied, which was monitored by measuring

and analyzing a series of parameters such as air

temperature, relative humidity and absolute pressure.

The results were then compiled and compared to an

adjacent room in which no heating system was

installed.

The main contribution of this research was the

development and validation of a practical solution to

reduce thermal discomfort in the internal environment,

mitigating the need for major interventions. In this

way, the system was proved to be technically feasible,

which allows its future application on a large scale.

Following this introduction, this paper is structured

into four additional sectors. Section 2 presents the

conceptual background of the research based on a

literature review, which culminates in research

questions development. Section 3 describes the details

of the research methodology procedures. Section 4

presents research findings and discusses the

implications of the study results. Finally, Section 5

summarizes the study conclusions, as well as exposes

work limitations and directions for further research.

2. Conceptual Background

Architecture has the mission to protect humans

from external undesirable conditions, providing a

comfortable and functional indoor habitat. In turn,

bioclimatic architecture proposes to solve these issues

using strategies that take advantage of local climatic

conditions, trying to reduce to the maximum the use

of equipment powered by electricity or any other kind

of fuel. Thus, thermal comfort and the use of passive

systems to solve this problem are directly linked to

sustainability and cost reduction. In fact, once

buildings begin to use passive heating or cooling

systems, they reduce their dependence on air

conditioners and heaters, contributing to a healthier

environment and ensuring lower rates of electricity

consumption.

The definition of the most suitable bioclimatic

architecture strategies for a given region depends on

the evaluation of the climatic conditions of the place

where the intervention will be carried out. These

environmental conditions, more specifically, wet bulb

temperature, dry bulb temperature and relative

humidity, are used as input variables in bioclimatic

diagrams, which indicate the best strategies to achieve

thermal comfort within a building [9]. Over the years


several researchers have developed their own

diagrams and the most widely used was the one

proposed by Olgyay [2], which was officially adopted

by ASHRAE (American Society of Heating,

Refrigerating and Air Conditioning Engineers) [10].

In Brazil, the instrument proposed by Baruch Givoni

[3] is the most applied one and is based on the same

above mentioned parameters (Fig. 1).

The input of the variables in the graph will indicate

a point, which will invariably be located within one of

the fourteen existing areas. The area delimited by

green indicates the comfort zone, which means that

for these climatic conditions the architecture design

does not need to perform any thermal correction. Any

point outside the comfort zone indicates that

architectural strategies must be implemented to reach

thermal comfort. Since the city of Petrópolis, where

the residence used in this case study is located, is

classified in zone 4 of the Givoni [3] chart, this paper

analyzed the possible passive solar heating systems

that could be applied.

2.1 Passive Solar Heating

Passive solar heating is the technique that aims to

reach the comfort zone absorbing the energy of the

sun by means of strategies that allow the thermal

energy gain within the space. According to Ref. [11],

the term passive refers to the envelope design of the

building, which acquires special relevance during the

winter months, when temperatures drop and solar

gains must be maximized, so that solar radiation can

be accumulated and then shared with other

dependencies of the building [12].

There are different models of passive systems. Figs.

2 and 3 illustrate the direct gain model, where the

energy distribution occurs by radiation (temperature

gradient) and convection (heating of the air in contact

with the emitting terrain), respectively [13].

Fig. 1 Psychrometric chart [3].


Fig. 2 Direct gain by radiation.

Fig. 3 Direct gain by convection.

The energy distribution can also indirectly force air

through elements that accumulate heat and

subsequently circulate in the room [13]. A classic

example of this indirect model is the Trombe wall.

According to Ref. [14], “A Trombe wall is a

south-facing concrete or masonry wall blackened and

covered on the exterior by glazing. The massive

thermal wall (storage wall) serves to collect and store

solar energy. The stored energy is transferred to the

inside building for winter heating”. Fig. 4 shows how

the Trombe wall operates, where air is heated up by

the wall, flows upwards and then returns through the

top vent [14]. A Trombe wall system is quite similar

to the greenhouse effect system, where a room with a

large sun exposure can provide part of the heating

needs of its neighboring spaces. The room receives

solar energy and transfers that energy to adjacent

rooms by conduction or through openings in a

common wall (Fig. 5).

The research aims to investigate the interaction of

the built environment with the climate of the region

and to discover the best passive heating system to

mitigate thermal discomforts. In order to achieve this

objective, it was necessary to answer the following

research questions (RQ) by means of a quantitative

study, as outlined in the next section.

RQ1: Why solar energy captured during the day is

lost even before nightfall?

RQ2: What is the most interesting passive heating

system to be applied in this case study?

RQ3: Has the proposed system actually improved

the thermal comfort of the studied room?


Fig. 4 Trombe wall system.

Fig. 5 Greenhouse effect.

3. Method and Materials

The current case study adopts a quantitative

methodological approach (Fig. 6) in order to increase

research reliability. The first step was the selection of

the ideal site for the study. The Brazilian city of

Petropolis, located in the state of Rio de Janeiro, was

chosen because it presents a favorable climate for the

use of passive heating systems, since it presents

summers with mild temperatures and strict winters, with

average temperature of 10 °C in the coldest months.

The second step was the selection of the building to

be studied. The residence has three floors built in

masonry and wooden windows and doors. The third

step of the research was the selection of the rooms

where the measuring points were installed. In this

sense, a solar chart was developed to identify the

trajectory of the incident sun on the vertical surfaces

of the residence (Fig. 7), so that it was possible to

determine the façades with higher solar incidence

during the day, mainly in the afternoon, taking

advantage of this resource to the maximum. Then, two

adjacent rooms were chosen, both located on the same

facade, which receives more sunlight.

Fig. 8 presents the two selected rooms. The room

marked in blue did not receive a heating system, while

the room marked in pink was chosen to receive the

intervention proposed by this study. After choosing

the rooms to be studied, the fourth step was to identify

the best passive heating system to be used in this case

study. An analysis of the constructive parameters of

the building was made and it was observed that the

major problem came from air infiltration through

windows without adequate sealing. The presence of


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Fig. 6 Adopted methodological trajectory.

Fig. 7 Solar chart for the studied building.

Fig. 8 Floor plan of the studied building.


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openings up to 2 cm wide promotes rapid and intense

heat loss, analogous to passive cooling. However, in

this particular case, this passive cooling is undesirable

due to the low temperatures presented by the region.

The proposed system is intended to heat and not to

cool.

Thus, in addition to enabling the response of RQ1,

the discovery of the cause of the heat loss allowed the

definition of the greenhouse system as the most

appropriate for this situation, because in addition to

storing the heat from the sun, this system prevents the

infiltration of air, since a perfect seal of the internal

and external environment is performed, minimizing

the heat losses in the night, which is the biggest

problem faced by the residence, thus responding to

RQ2. In this way, the system will contribute to the

thermal comfort of the residence, as well as to the

well-being of its residents.

The fifth step was the development of a prototype

that would maximize the occurrence of the greenhouse

effect in the room. For this purpose, a glass box of

1.33 m long by 1.15 m wide and 0.15 m thick was

constructed, presenting an air volume of 0.23 m3. This

glass box (Fig. 9) consists of an aluminum structure

that supports six millimeters thick glass plates, around

a window oriented to the facade with greater solar

incidence during the day, causing the desired

greenhouse effect.

After the prototype installation, two measurement

points were selected (white circles), one in each room,

according to Fig. 8. Thus, the sixth stage of the

research consisted of monitoring the two rooms,

measuring a series of parameters such as air

temperature, relative humidity and absolute pressure.

Normally the relative air humidity does not present

significant variations according to the measurement

device location in the studied space, however, the

other variations monitoring should be carried out with

greater caution, since the instrument position can

influence the result of the measurements. Therefore,

the apparatus positioning in the two rooms was

performed in a uniform way, that is, in the center of

the room, 1.5 m from the window and 1.10 m from the

ground. Measurements were taken at one hour

intervals over a 24-hour period. Finally, in the

eleventh stage of the study, the results were compiled

and analyzed to evaluate the effectiveness of the

system.

Fig. 9 Passive heating system prototype.


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4. Results and Discussions

After 24 hours of measurements, a set of indices

was obtained for air temperatures, relative humidity

and absolute pressure in each studied room. These two

last parameters did not present significant variations;

however, the air temperature did indeed vary

considerably, being represented in Table 1. Readings

were performed in each room with windows and doors

closed. The air temperature in the external

environment was also checked hourly, in order to

allow comparison and verification of the system

effectiveness. The instrument used in the

measurements was the thermal stress meter, model

AK887, brand AKSO, and readings were carried out

on May 4, 2019, which corresponds to half of autumn

in the southern hemisphere.

The analysis of Table 1 shows that Room 1, which

received the passive heating system, remained warmer

than the external environment throughout the

measurement period, while Room 2, which received

no intervention, presented lower temperatures than the

external ambient, resulting in thermal discomfort for

its occupants.

Thus, through the analysis of Table 1 last column, it

is possible to observe that the glass box

implementation around the window in order to reduce

heat loss through air infiltration and increase solar

energy capture promoted a constant positive

difference in the air temperature between the

environments with and without the heating system.

This can be especially verified between 12:00 and

15:00, when the solar incidence on the façade of the

building reaches its maximum value (Fig. 10).

Fig. 10 presents the air temperature variation in the

external environment and in Rooms 1 and 2. The

Table 1 Air temperature (°C) oscillation in the studied environments.

Measurement time External environment Room 1 (with the system)

Room 2 (without the system)

Differential temperature (Room 1-Room 2)

01:00 23.9 24.3 23.5 0.8

02:00 24.0 25.1 24.0 1.1

03:00 24.0 24.6 24.0 0.6

04:00 23.8 24.4 24.0 0.4

05:00 23.8 24.3 23.9 0.4

06:00 23.8 24.2 23.8 0.4

07:00 23.7 24.0 23.7 0.3

08:00 24.1 24.3 24.1 0.2

09:00 24.5 26.0 24.1 1.9

10:00 24.6 25.3 24.2 1.1

11:00 25.0 25.5 24.3 1.2

12:00 26.0 28.0 24.6 3.4

13:00 25.6 26.4 25.4 1.0

14:00 25.4 27.5 25.0 2.5

15:00 25.3 29.4 25.3 4.1

16:00 26.0 26.2 25.1 1.1

17:00 24.9 26.7 24.9 1.8

18:00 24.9 25.3 25.2 0.1

19:00 24.2 25.7 24.2 1.5

20:00 23.8 25.3 24.2 1.1

21:00 23.9 24.5 24.0 0.5

22:00 24.2 24.8 24.2 0.6

23:00 23.3 25.6 24.4 1.2

24:00 23.8 25.0 24.5 0.5


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Fig. 10 Air temperature variation in the external environment and in Rooms 1 and 2 over the 24 hours of measurements.

internal temperature increase of Room 1 is expressive

due to the glass box implementation, reaching a

maximum difference of 4,1 °C in relation to Room 2

at 15:00. The smallest temperature difference between

the two rooms was recorded at 18:00, when

temperatures nearly equaled. However, it is important

to note that Room 1 still remained warmer than Room

2 throughout the night, confirming the technical

feasibility of the proposed system and thus responding

to RQ3.

5. Conclusions

The evolution of the built environment is

intrinsically related to the efficient use of energy, and

an increasing amount of scholars have been devoting

themselves to the study of new materials and

techniques that can reduce the need for energy

resources without causing thermal discomfort in its

occupants. This phenomenon indicates that there is a

growing consensus on the relevance of the

construction sector as a promoter of sustainable

practices, since it accounts for a considerable share of

global energy consumption. In this sense, the research

findings not only significantly increase the existing

body of knowledge on energy efficiency, but also

provide practical support for the selection of passive

heating systems in regions with a humid subtropical

climate and a rigorous winter.

This study successfully answered the three research

questions providing practical implications for

engineers, architects and researchers. The

environment was analyzed and it was concluded that

there was permeability between the internal and

external environment, enabling air infiltration and

preventing solar heat retention. A greenhouse system

was then selected since it stores the incident solar

energy in the window during the day while it stops the

infiltration of air, allowing to retain the heat and to

warm the room. A prototype was then built and

installed in one of the rooms of the residence, while

another remained without interventions. After 24

hours of measurements, it was concluded that the

passive heating system installed effectively promoted

an increase in the air temperature, providing greater

thermal comfort to its occupants.

This research is subjected to some limitations that

should be considered, and some may serve as a

stimulus for future work. The research design

provides a snapshot of a specific room, in a specific

residence and in a specific climate; therefore, further

studies could test the system applicability in different

locations. The research findings are also clearly

limited in terms of sample size. Although 24 hours is

considered an acceptable period of time,

generalization of results should be done with caution,

since it does not represent all possible climatic


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variations. A more extensive sample should be

considered in future studies to overcome this problem.

Associated with this limitation is the fact that the

orientation of the sample was done in a partial way. In

fact, rooms located on the diametrically opposite

facade to those selected may present different results,

but the investigation of these differences was not

included in the scope of the article. For future research,

it would be also interesting to examine the behavior of

the studied environments during the winter, since this

study was realized in autumn.

Finally, current research can be extended in several

directions; however, it is important to emphasize the

need to invest in better sealing projects since an

improvement in the window frames performance can

minimize the need for passive heating systems.

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Passive Heating Systems: A Case Study in a Brazilian ... · bioclimatic building design. His method was based on a “bioclimatic chart” showing the human comfort zone in relation