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TRANSCRIPT
Indoor thermal comfort by controlling heat transfer
through building envelope
DANIEL POPESCU1 and CALIN CIUFUDEAN
2
1Electrical Engineering Department
Technical University of Civil Engineering Bucharest
Bd. Pache Protopopescu nr.66, 021414 Bucuresti Sector 2
ROMANIA
2Computers and Control Systems Department
“Stefan cel Mare” University of Suceava
Str. Universitatii nr.9, 720225 Suceava
ROMANIA
Abstract: The assurance of thermal comfort in buildings with heating / cooling installations distributed on the
surface is the best common solution.
This article proposes a new approach for analyzing the heat transfer through building envelope. Our approach
consists in a distributed area of electro-thermal pumps over the building envelope capable to create antagonist
thermal fluxes to those that appear naturally. In this way we can easily control the inside temperature by
balancing the dynamic of heat transfer. The electro-thermal pump works by relying on the Peltier–Seebeck
effect. The thermal flux direction is given by the electric current direction.
Building envelope equipped with electro-thermal pumps is the process who must to be controlled automatically
by temperature control system dedicated.
The goal of this new concept is to optimize the thermal comfort, eliminate the moisture condense on the walls
and reducing the energy consumption by controlling the building’s envelope temperature.
Key-Words: thermal comfort, heat transfer, building envelope, HVAC (heating, ventilation, and air
conditioning), automatic control of heating systems of buildings, thermoelectric systems, electro-thermal pump.
1 Thermal comfort in buildings
with heating / cooling
installations distributed on the
surface 1.1 Temperature profiles and distributed
heat sources in buildings Energy saving for heating/cooling buildings
requires a fair thermal insulation of the buildings.
On the other side there is a maximum optimal size
of the thermal insulation.
Inner thermal sources balance heat loss and keep up
to the required comfort parameters. These sources
are concentrated in certain areas (heating radiators,
fan coil), therefore the comfort parameters may
vary in different places under discontinuous
functioning regimes. Therefore, distributed heat
sources made in floor, ceiling or walls are
increasingly used [1, 10].
16° 20° 24° 16° 20° 24° 16° 20° 24° 16° 20° 24°
1,80 m
0,10 m
Ideal
heating
Underfloor
heating
Radiator
outer wall
Radiator
inner wall
Fig.1 The „temperature profile“from floor
to ceiling
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Figure 1 shows „temperature profile“ from floor to
ceiling for ideal heating system, with „temperature
profiles“ for under floor heating and wall mounted
radiators [2, 3]. Note that the floor heating system
ensures the best thermal comfort in building.
Figure 2 shows how to make the system of
heating / cooling floor [2].
Fig. 2 Under floor heating in a room
Desire to improve indoor thermal comfort in
buildings led in some cases to achieve the system
as wall heating / cooling (Fig.3). Under floor
heating elements are suitable for wall
heating/cooling systems.
Fig. 3 Wall heating system
1.2 The thermal insulation of surface for
heating / cooling Thermal insulation of floors used as surface
heating/cooling must accomplish certain
requirements, depending on the location in the
building floor (below room temperature) [2]:
a) surface heating above a heated room
(≈200C);
b) surface heating above a room
heated in irregular intervals (≈150C);
c) surface heating above a cellar (unheated
basement) (≈80C);
d) surface heating in direct contact
with outside air or ground;
Figure 4 shows how to make the thermal insulation
for heating / cooling systems, the first two cases
[2]:
a) Surface heating above a heated room (Fig.3,a)
- Insulation layer 35mm
- Thermal resistivity R ≥ 0,75 (m² K) / W
b) Surface heating above a room
heated in irregular intervals (Fig.3.b)
- Insulation layer 35 mm
- Additional insulation layer 20 mm
- Thermal resistivity R ≥ 1,25 (m² K) / W
+ 20 °C
+ 20 °C
hE
hD
hB
+ 20 °C
+ 15 °C
hBhE
hD
hZ
Fig. 4 Under floor heating - thermal insulation
a) hB = Floor covering hE = Screed
hD = Insulation layer
b) hB = Floor covering hE = Screed
hD = Insulation layer hZ = Additional
insulation
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Heating or cooling surfaces made in floor, ceiling
or walls can contribute to heat transfer through
building envelope.
2 Improving temperature control
systems performance for heating
under floor Under floor heating system is designed to ensure
room temperature of 200C if the temperature of
thermal agent in the flow pipe is 26 ÷ 270C.
The occurrence of additional heat input into the
building (eg the sun) will lead to overcoming the
room temperature of 200C and, therefore, the room
thermostat will stop the under floor heating for a
while (Fig.5). According to the classical method of
control, the under floor heating circuit is closed and
the flow of thermal agent is zero (Fig.6). Room
temperature will drop to a value of 200C and the
under floor heating must start now.
Total absence of heat flow (thermal agent with flow
zero) has cooled too much the floor and the time
response to turn on the under floor heating is too
large. The overshoot may be unacceptable and floor
temperature may be too high during certain periods
of time; human health may be affected, increase
comfort and decrease energy consumption of
building heat.
30 % outside heat
T = 21 °C > Tset
Heat flow from the
floor surface = 0 %
Heating circuit
closed
Operation with secondary heat source
- no flow rate in the heating circuit
- floor surface is cooling down
Fig. 5. Regulation of the under floor heating
by using the room temperature control
Fig. 6 Under floor heating with room thermostat
Current requirements increase thermal comfort in
buildings, along with requirements to reduce
energy consumption for heating led to the use of an
automatic control method for under floor heating
system, where the residual flow heat in the under
floor heating circuit remains constantly [2 ,4] when
the system is stopped (Fig.7, 8).
30 % outside heat
T = 21 °C > Tset
Heat flow from the
floor
surface = 70 %
Heating circuit
open
Operation with secondary heat source
- Thermostatic valve closed
- Bypass open
Fig. 7 Regulation of the under floor heating
by using the preset table bypass
The preset table bypass provides a
constant residual flow in the circuit and
therefore a minimum floor temperature. It reduces
the time for heating up by
1 ½ h [2].
Thermostat
Preset
table
bypass
Under floor
temperature
Volume
flow
Heating circuit closed
200C
300C
Time
Temperature [0C]
Volume flow [m3/h]
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Fig. 8 Under floor heating with preset table bypass
The preset table bypass prevents the floor from
cooling down too much, in case of the thermostat
isolating the heating circuit due to a secondary heat
source [2].
3 Electro-thermal pump distributed
on the surface Thermoelectric materials may have an important
role for a global sustainable energy solution.
The electro-thermal pump (Fig. 9) works by relying
on the Peltier–Seebeck effect: on an electrified
serial junction of two different metals (e.g. metals
with different electron charges) we obtain different
temperatures, respectively on obtain heat flow.
The electro-thermal pump distributed on the
surface as is composed of semiconductors plates
applied on the inner surfaces of the walls has no
kinetics elements and also occupies little spaces.
The heat transfer through the building’s envelope
depends on the electric current intensity delivered
by the thermal elements and is controlled by a
computerized control unit.
The electro-thermal pump is reversible: the thermal
flux direction is given by the electric current
direction.
In present, a lot of projects were selected to
accelerate the development of thermoelectric
systems that provides the heating, ventilation, and
air conditioning (HVAC) for automotive industry.
The use of solid state thermoelectric devices to heat
and cool a vehicle’s passenger compartment can
increase vehicle efficiency by reducing engine load,
by reducing or eliminating the need for
conventional air conditioning refrigerants, these
vehicles further reduce greenhouse gas emissions.
Thermoelectric HVAC enables the use of
distributed cooling/heating units that cool/heat the
occupants rather than the whole cabin and its
components [10].
Fig. 9 Electro-thermal pump
While applicable to all commercial and passenger
vehicles, thermoelectric HVAC is particularly
attractive for hybrids and plug-in hybrids where an
electrically driven air conditioning system can
maintain occupant comfort even when the engine
turns off.
Research direction is to develop a system
thermoelectric HVAC that provides thermal
comfort equivalent to current HVAC systems while
using significantly less energy. The thermoelectric
system components will be integrated into a
demonstration vehicle for testing and evaluation.
4 Automatic control of heat transfer
through building envelope Indoor thermal comfort and energy consumption of
buildings depends on the heat transfer by building
envelope [5].
Volume
flow
Under floor
temperature Heating circuit
partially closed 200C
300C
Time
Temperature [0C]
Volume flow [m3/h]
30% residual flow
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4.1 Infrared thermograph method of
building envelope Between the period 2007 – 2008 at the Technical
University of Civil Engineering Bucharest was
developed a research grant concerning the
automatic control of heating systems of buildings
by measuring the heat transfer through outside
bulding surfaces.
As a result of the research work for this grant there
have been designed and implemented an automat
control system that measures the heat transfer
through the building walls [6, 7. 8]; so that one may
thermo graphically measure the temperature of the
exterior walls and by converting from analog to
numeric the measured values one may control the
thermal confort through a computerized system
which control the debit of thermal agent inside the
bulding.
Automatic control basically consists on regulating
the flow of the thermal agent as a function of heat
loss through the exterior walls of the building. In
order to have an accurate control one may have to
supervise the temperature fluctuation at the surface
of the exterior walls. This process involves
experimentally charting the temperature of the
exterior walls and memorizing it into the
computerized control systems, such that any
changes in temperature distribution through the
walls surface is sesized by the control system
which will act on the thermal agent debit
accordingly [8].
4.2 Automatic control of heat transfer
through building envelope with electro-
thermal pump distributed on the surface This article proposes a different approach for
thermal transfer through buildings envelopes [9],
namely by surface distributed electro-thermal
pumps which control heat transfer through
envelope.
The above-mentioned approach is possible by
heating thermal flows opposite to natural flows
which will determine a controlled temperature
balance of the building’s inner walls.
This new approach will ensure the thermal comfort
as an alternative to the conventional heating
methods of buildings.
The solution is based on achieving an electro
pumps distributed on the surface, which controls
the heat transfer through the building’s envelope.
This new approach will ensure the thermal comfort
as an alternative to the conventional heating
methods of buildings eliminate condensation in
walls and reducing energy consumption in
buildings through building envelope temperature
control. It acts directly on the building envelope
that is the part of the building which loses heat to
the outside.
The thermoelectric elements are placed on different
types of materials constituting the walls of
buildings in order to obtain a homogeneous
temperature distribution. For walls equipped with
thermoelectric elements heat transfer is evaluated
by thermograph method.
Among those models who we studied, we choose
those that could withstand the winter and summer
weather, i.e. heating and cooling regimes and
determine the extreme limits of operation.
The building envelope equipped with electro-
thermal pumps is the process to be controlled
automatically with a dedicated temperature control
system.
5 Conclusions The new concept proposed allows obtaining the
same temperature inside the building envelope,
regardless of the orientation of the walls, so
basically dynamics of heat transfer through the
inner walls of the building depends only on
evolution of internal sources of heat.
Thermal insulation of building envelope can be
greatly reduced.
By adjusting the building envelope temperature is
obtained a good indoor thermal comfort, is
eliminated the condensation in walls and energy
consumption in building is reducing.
Control of heat transfer through building envelope
by using electro-thermal pumps distributed on the
surface can replace total or partial traditional
heating / cooling systems, remain to be used only
fresh air-conditioning systems that ensures indoor
air quality.
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ISBN: 978-1-61804-099-2 155