Design and Automation of Passive Ventilation to a NZEB School Classroom

8/9/2019 Design and Automation of Passive Ventilation to a NZEB School Classroom

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Design and Automation of Passive Ventilation to a NZEBSchool Classroom

Artur Ribeiro

1

, Jos Baptista

2

, and Joo Ramos

1,3

1Institute for Systems Engineering and Computers at Coimbra, INESC Coimbra, Portugal.

2Dept Engineering, Univ. de Trs-os-Montes e Alto Douro, Vila Real, Portugal.

3Dept. of Environmental Engineering, Polytechnic Institute of Leiria, Leiria, Portugal.

E-mail: [email protected]

Abstract

The application of passive techniques in buildings, which stands the incorporation of renewable energy,

complemented by active systems creates a high potential self-sustainability in particular in school buildings

[1]. The automation of passive and active systems, through centralized management techniques, led us to

create an integration of actuators with innovative natural ventilation systems and renewable energy

production in a school, making it possible to obtain a school building as NZEB (Net Zero Energy Building)

[2]. In the current study, a classroom was in particular simulated. The natural ventilation was promoted

through four records facades, located respectively at the bottom and top, within an air collector composed by

PV modules in the front. The records were operated automatically by two actuators, one linear and other

rotational, thereby optimizing the energy performance of the building. To obtain cross-ventilation, a flag of

thin steerable glass was raised on the top of the door of each classroom. A air ground heat exchanger,

allowing the introduction of new air in the classroom for heating or cooling was also implemented. These

are obvious advantages for the process of heating and cooling, provided by automatically controlled

actuators in the ventilation ducts records. The energy assessment, with the integration of active and passiverenewable energy production systems and controlled ventilated techniques, demonstrated the excellent

building performance, where the balance between the annual energy supply and the building demand is

equal to "Zero Energy and "Zero Carbon.

Key words: Air-Ground Heat Exchanger, Centered Technique Management, Passive Ventilation, PV Air

Collector, NZEB.

Implementation

This work was carried out to study the energy and

environmental performance of a new school building located in Alcobaa (Portugal) [1]. An

energy balance was done and, in particular, a study

of the use of passive techniques, like the

incorporation of renewable energy, complemented

by active ones and centralized management

technique was analyzed to evaluate the potential of

self-sustainability of the school building. The windaction analysis is very important in the natural

ventilation characterization. To protect the building

from the prevailing winds and decreased radiant

temperature was used a live hedge composed of

persistent leaves (Figure 1).

Figure 1: Vegetation scheme to protect the building from the prevailing winds.


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Native species were chosen because of their low

porosity which is achieved in the implementation of

a hedge, reducing wind speed to 90%. [4] [5] [6].

The wind drags are caused by the building, to

reducing wind speed to 50% [7] [8] [9] [10] [11]

[12].

For this study a specific classroom with 56 m2

and

natural ventilation system was selected. The facade

is composed by an air collector with four openings

(automated faade records) in each classroom

section, two 20 cm below the floor level and two at

the top, 50 cm above the false ceiling. The air

collector (Figure 2) is composed by 6 PV modules,

mounted on an aluminum structure, arranged in N-S

direction and distanced 10 cm from the wall.

Figure 2: Records positions for different weather conditions operation.


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The records of facade implemented here were

developed by [13], the building Solar XXI, which is

manually manipulated by its users. This study

intended to automate its operation, with two

actuators, one linear and one rotational in each

record, optimizing its use.

A flag is placed in thin steerable glass in each

classroom door, to obtain a cross-ventilation effect.

The flags are opened or closed depending on the

temperature, humidity and indoor air quality,

compared with outside temperature and humidity,

measured by sensors installed therein. The cross-

ventilation effect can be complemented with the

chimney effect, by using the adjacent movement

corridors. They are vertically connected through a

duct across the length and forming a projection on

the southern side of the roof. On this side the

ventilation grilles are also established (Figure 3).

The chimney effect can be increased through a

higher temperature in the duct, obtained by placing

a polished aluminium plate liner in the last 2 m. The

air ground heat exchanger, allows clean air to enter

the classroom through concrete pipes buried at 3 m.

This air can be used for heating or cooling,

depending on the season, since the conditions of thetemperature at the burial are almost constant. These

are obvious advantages for both, the heating and

cooling process, being controlled by actuators on

registration circular ventilation ducts. The spread is

produced by a fan, that is mounted axially above a

metal ring duct, with 65 cm axis, above the floor,

only serving as a complement to ensure indoor air

quality in situations lacking wind on the outside or

when CO2 level is achieving the regulatory limits

[14] (Figure 4).

The centered technique management allows all this

automatic manipulation but only some parameters

can be modified by users in a short period of time,

after which the management takes control.

The systems described, will be presented in more

detail the air-ground heat exchanger, keeping in

mind their design based on three main aspects: the

exterior temperature, the soil temperature at the

exchange depth and, not least important, the

exchangers characteristics, inter-related with the

first two. In the absence of meteorological data or

series of local climate, the exterior temperature can

be determined by (1) [15]:

For the location being studied synthetic

meteorological data is available from the climate

"Solterm 5" database [3]. The undisturbed soil

temperature at a certain depth, is determined by its

average temperatures existing in NASA climate data

(3). [15] [17]

The determination of air temperature at the exit of

the tube, allow the dynamic quantification of the

energy saving by the heat exchange. For this was

used mostly the same formulation in theEnergyPlus

[C] (1)

[C] (2)

[C] (3)

Figure 3: Integrated system of natural ventilation and

lighting systems with facade PV air collector and air-

ground heat exchanger.


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model [18], for more detail to quantify the

contribution of soil and material used in the

exchange. Here is the efficiency system key, so it

appears that the parameters used, were changing

depending on the exterior temperature, the

simulation to a dynamic component, absent in other

studies conducted so far. So we present in the

following equations parameters with variability

depending on the temperature. [18] [19] [20] [21]

[22]

[Pa.s] (4)

(5)

[W/mC] (6)

(7)

(8)

(9)

[W/mC] (10)

Using the three thermal resistance values, Rc, Rp

and Rs, the total heat transfer tube coefficient of the

earth can be estimated as follows: [22]

[W/mC] (11)

[W/mC] (12)

[W/mC] (13)

[W/mC] (14)

(15)

Was considered by [17] [19], that the soil is

undisturbed in the role of exchange, until r3 = 2r1.

With NUT, is obtained the air temperature leaving

the heat exchanger. [15]

[C] (16)

With the previous parameters is determined by the

gross energy order obtained by the system. [15]

[W] (17)

The loss of load in the pipe can be determined bythe following expression: [22]

[Pa] (18)

The heating system of air efficiency, resulting from

the soil exchange is like: [23]

[%] (19)

The heat exchange operation in each of the systems

(Heating / Cooling / Off) will be controlled by the

centralized management technique. One of the

criteria implemented for the air ground heat

exchanger was not to cause overheating or

undercooling the interior of the space served. That

operation it is possible only within the marked areas

on the graph of Figure 5. These are inter-related

with the inside comfort temperature, exterior

temperature, average day temperature and the heat

Figure 4: Front view (left) and cut (right) of the duct

and spread of air-ground heat exchanger system in

floor 0.

Figure 5: Outlet air temperature in the heating

(up) and cooling (down) seasons.


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exchanger outlet air temperature. To implement this

formulation we used the parameters described in the

following tables [15].

Table 1: Constants used in the algorithm [15]

Description Unit Value

Cp ar J/(kg.K) 1007

Density of air kg/m3 1,2

0 dynamic viscosity of air reference [21] Pa.s 18,27E-6

T0 temperature of reference K 288,15

C gas constant of Sunderland [21] - 120

Table 2: Values for the soil used in the algorithm [15]

Soil typeDiffusibility

(m2/h)

Conductivity

(W/m K)

Density

(kg/m3)

Wet clay soil 0,0023 1,298 2105

Results

The use of models in the spreadsheet allows a pre-

feasibility analysis to give to the building designers

quick solutions to choose this systems liabilities

introduction. The air-ground heat exchange design

is based on three main aspects: The exterior air

temperature, the ground temperature at the

exchange depth and, not less important, the

exchangers characteristics that interrelated with the

first two. This platform is easier to access than other

specific calculation dynamic program. The

exchange system operation will be controlled by

centered technique management, by criteria that

prevent over heating or under cooling in the interior.

The simulation was implemented based on

Retscreen [24] methodology, recently introduced

in Portugal by [15]. It was intended to improve the

simulation method and endow it with tools capable

of determining with more detail the gross profits

transmitted for the building that can be introduced

in thermal building calculation. The passive cooling

system is composed by cross-ventilation, heat

chimney effect, air-ground heat exchanger and air

collector facade. Without any mechanical cooling

systems, it is able to create comfortable conditions

in the interior, because of the thermal amplitude

between exterior and into burial pipes temperature

that can reach an average of 10 C. These conditions

are achieved by cool flow air diffusion through the

air-ground heat exchanger and its diffusion by

thermal effect of cross ventilation to the duct in the

corridor or air collector facade. Thermal building

calculation [25] gives us the values of the primary

energy global needs, Ntc = -5,33 (kgep/m2.year) and

a ratio between these and its legal limit in Portugal,

R= -3,37. In the same way, systems energy and air

conditioning building calculation, in monozonetypology [26], was based on the simplified method

of global conversion factor. For these, primary

energy annual consumption energy was calculated.

In this calculation the specific energy building

consumption Cei = -0,01 (kgep/m2.year) and a

energetic efficiency index IEE = -0,01 values were

obtained.

Conclusions

A ground heat exchanger allows the introduction of

new air in to the classroom for heating or cooling,

depending on the season, since the conditions of

temperature at ground level are almost constant.

These are then obvious advantages both for the

process of heating and cooling, being controlled by

actuators on circular ventilation ducts registration.

Although the air ground heat exchanger by itself,

cannot replace a system of conventional air cooling,

it can significantly reduce the load cooling of the

building. For better performance in cooling, the pipe

used should be buried deeper, with more length,smaller pipe diameter and low air velocity.

Furthermore, if the main objective is to reduce the

need for heating burial near the surface should be

used, to receive the radiation incident on the Earth's

surface, thereby acting on the role of increased air

collector. In this study the main objective was the

cooling needs, so we opted to burial 3 m depth. Less

electric production of the facades, caused by the

photovoltaic system, was counterbalanced by the

classrooms internal thermal profits improvement,through the associated air collector. To achieve anFigure 6: Initial sheet program for simulation of air-

ground heat exchanger.


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Net Zero Energy Building (NZEB) classification [2]

it was also important to conjugate the efficient

equipment with passive cooling and heating

techniques, controlled through centered technique

management.

NomenclatureTaannual - mean annual temperature;

Amp adiria - amplitude of daily temperature in warmer months;

Amp aanual is the amplitude of annual temperature, based on the

maximum and minimum monthly average;

fasediria - time to adjust the hottest hours of the day;

faseanual - time to adjust the hottest hours of the year;

t - time of the year on the basis 8760;

Ts(t,z) - temperature of the soil to depth of burial in time t;

Tsanual - average temperature of the soil;

Amp sanual - amplitude of annual temperature of the soil, based on the

maximum and minimum monthly average;

- thermal diffusibility the soil;

z - depth of burial of the heat exchanger air to ground;

- dynamic viscosity of air;

0 - dynamic viscosity of air in the reference Pa.s;

T0 - reference temperature in K;

Ta - outside air temperature in K;

C - gas constant of Sunderland;

Re - number of Reinolds the pipe;

- density of air;

V - air speed;

D - internal diameter of the tube;

ka - thermal conductivity of air;

Pr - Prandtl number;

Cp - thermal capacity of air [J / Kg.K];

fa - roughness factor of the tube;

Nu - Nusselt number;

hc - coefficient of thermal convection of air inside the tube;

r1 - radius of the tube [m];

r2 - thickness of the tube [m];

r3 - distance between surface of the tube and the undisturbed soil [m];

L - length of the tube;

kp - thermal conductivity of the tube;

ks - thermal conductivity of soil;

Rc - strength of convection;

Rp - resistance of the driving tube;

Rs - resistance of the soil driving;

Ut - coefficient of thermal transfer of the heat exchanger;NUT - number of transfer;

Ts -temperature of the soil to depth of burial;

Tp - air temperature leaving the heat exchanger;

q - gross energy produced in the system of exchange;

n - number of parallel tubes in the system.

References[1] Ribeiro, Artur; Concepo de Edifcios Energeticamente Eficientes

com Incorporao de Energias Renovveis (Dissertao de

Mestrado); UTAD; Vila Real; 2008;

[2] Voss, Karsten; Towards net zero energy buildings; University

Wuppertal - CYTED - Os Edifcios Bioclimticos a integrao das

Energias Renovveis e os Sistemas Energticos; Lisboa; 2008.

[3] Solterm 5.0 - Anlise de desempenho de sistemas solares trmicos e

fotovoltaicos; INETI.

[4] Brandle, James R.; Zhou, Xinhua; Hodges, Laurie; How windbreaks

work - EC1763; University of Nebraska; Lincoln; 2005.

[5] D. L. 565/99, Introduo na natureza de espcies no indigenas da

flora e fauna; Dirio da Repblica; I srie; 21/12/1999.

[6] Farmstead windbreaks: Planning; Iowa State Univ.; Amnes; 1997.

[7] Allard, Francis; Natural ventilation in buildings - A design

handbook; European Commission - Directorate-General for energy,

altener program; London; 1998.

[8] Lee, Sang-Joon; Lim, Hee-Chang; A numerical study on flow

around a triangular prism located behind a porous fence; Fluid

Dynamics Research - Elsevier; Amsterdam; 2001.

[9] Li, Wei; Wang, F.; Bell, S.; Simulating the sheltering effects of

windbreaks in urban outdoor open space; Journal of Wind

Engineering and Industrial Aerodynamics - Elsevier; 2007.

[10] Plate, Erich J.; The aerodynamics of shelter belts; Agricultural

Meteorology - Elsevier; Amsterdam; 1970.

[11] Sldek, I.; Kozel, K.; Janour, Z.; Mathematical modelling of

atmosferic flow over a shelter-belt; Wiley-VCH; Weinheim; 2006.

[12] Wilson, John D.; Numerical studies of flow through a windbreak;

Journal of Wind Engineering and Industrial Aerodynamics -

Elsevier; Amsterdam; 1985.[13] Gonalves, H.; Edifcio Solar XXI - Um edifcio energeticamente

eficiente em Portugal; INETI; Lisboa; 2005.

[14] EN13779 - Ventilation for non-residential buildings - Performance

requirements for ventilation and room-conditioning systems; 2003.

[15] Monteiro, Mnica; Permutadores de calor ar-solo. Anlise da pr-

viabilidade (Dissertao de Mestrado); Univ. Aveiro; Aveiro; 2008.

[16] Site of NASA/ RETScreen (Searched in 2008);

http://eosweb.larc.nasa.gov/sse/RETScreen/ .

[17] Al-Ajmi, F.; Loveday, D. L.; Hanby, V. I.; The cooling potential of

earth-air heat exchangers for domestic buildings in a desert climate;

College of Technological Studies - Kuwait, Loughborough

University, De Montfort University, Elsevier; 2005.

[18] EnergyPlus engineering reference - The reference to energyplus

calculations; US Department of Energy - EnergyPlus, 2008.

[19] Lee, Kwang H.; Strand, Richard K.; Implementation of an earth

tube system into energyplus program; University of Illinois at

Urbana-Champaign; Champaign; 2006.

[20] Smith, R.; Sabarathinam, P.; A Simple and quick method of

estimating Prandtl number for fifty commonly used liquids; Journal

of the Institution of Engineers (India); 2006.

[21] Viscosity calculator; LMNO Engineering, R., S., Ltd; 2003.

[22] White, Frank M.; Fluid Mechanics; McGraw-Hill, 2000.

[23] Gieseler, U. D. J.; Bier, W.; Heidt, F. D.; Cost efficiency of

ventilation systems for low-energy buildings with earth-to-air heat

exchange and heat recovery; Conference on Passive and Low

Energy Architecture - France; Toulouse; 2002.

[24] Ground-source heat pump project analysis (Searched in

23/06/2008); www.retscreen.net

[25] D.L. 80/2006, RCCTE - Regulamento das caractersticas de

comportamento trmico dos edifcios; D. R.; I srie; 04/04/2006.

[26] D.L. 79/2006, RSECE - Regulamento dos sistemas energticos de

climatizao em edifcios; D. R.; I srie; 04/04/2006.

Design and Automation of Passive Ventilation to a NZEB School Classroom

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