Experimental Results for Ventilation System with Local ... · diffuser being less than 40 dB(A) for...

International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 21 (2016) pp. 10721-10730

© Research India Publications. http://www.ripublication.com

10721

Experimental Results for Ventilation System with Local Recirculation

Diffusers

Dmitry Vladimirovich Kapko,

LTD “NPO THERMEC”, 46-2, Dmitrovskoe shosse, Moscow 127238, Russia.

Vyacheslav Erikovich Shkarpet, Kristina Vladimirovna Kochariantc,

LTD “Arktos”, 4, Predportoviy proezd 6, Saint-Petersburg, Russia.

Iurii Andreevich Tabunshchikov, Marianna Mihailovna Brodach,

Moscow Architectural Institute (State Academy), 11, Rozhdestvenka street, Moscow 107031, Russia.

Abstract

The paper presents experimental results for a ventilation

system with local recirculation diffusers designed by the

authors for buildings with high heat emissions (˃ 25 W/m2),

such as office buildings. A 6,000 m3 office building in

Moscow has been demonstrated to have indoor excess heat

occurring at the outdoor air temperature over -9 °C. A

principal diagram of a ventilation system with the designed

local recirculation diffusers (LRD) is given.

Tests were carried out on aerodynamic and acoustic benches

and on a bench demonstrating the use of the designed system

in an office.

The tests have confirmed that comfort air temperature and

acoustic parameters can be ensured in a room serviced with a

ventilation system with local recirculation diffusers when the

outdoor air temperature supplied to the LRD is +6 °C and

above. It has been confirmed that a local recirculation

diffuser can automatically maintain comfort air temperature

parameters (air temperature range of 19 to 21 °C, air flow

velocity of 0.2 m/s max.) according to the outdoor air

temperature (outdoor temperature range of 6 to 18 °C) and

the room heat load (recirculation air temperature range of 18

to 25 °C), with the sound pressure level generated by the

diffuser being less than 40 dB(A) for a distance of 2-2.5 m.

Keywords: Ventilation systems, recirculation, local

recirculation diffuser, diffuser, energy efficiency,

experiment, acoustic test, aerodynamic test, full-scale test.

INTRODUCTION

At present, one of the most essential tasks for a designer of

ventilation systems is to achieve comfort air temperature

conditions at minimum energy consumption. A more and

more increasing number of theoretical and experimental

studies have been dedicated to upgrading the existing

systems and designing new schemes and solutions for

ventilation systems of buildings [1-9].

This article provides experimental results for a ventilation

system with local recirculation diffusers designed by the

authors. These systems are designed for buildings with high

heat emissions (˃ 25 W/m2), such as office buildings.

The main feature of these buildings is the occurrence of

indoor excess heat during a transitional period between

seasons and even during a heating period of a year.

According to the analysis conducted by the authors (Figure

1), the indoor excess heat in a 6,000 m3 office building in

Moscow occurs when the outdoor air temperature is above -

9 °C (mean indoor heat emissions in Russian office buildings

are 27.46 W/m2, including 5.4 W/m2 from people, 12.8 W/m2

from lighting, and 9.26 W/m2 from office equipment).

Figure 1. Comparison of the indoor heat emissions and the heat losses during cold and transitional periods for a 6,000 m3 office

building in Moscow

0

5

10

15

20

25

30

35

40

-21 -18 -15 -12 -9 -6 -3 0 3 6 9 12 15 18

Outdoor air temperature , ᵒC

Specific heat losses, W/m2 Indoor heat emissions, W/m2



10722

Figure 2. The principal diagram of a ventilation system with local recirculation diffusers

Reduction of the supply air temperature from the air supply

unit to values, at which the indoor excess heat can be

assimilated, thus reducing the heat consumption of a

ventilation system for heating the outdoor air, can be a

rational solution for these buildings. However, this reduction

is restricted by regulatory documents (in the Russian

Federation, this value is specified in a relevant Rulebook

[10]) so that comfort parameters of the supply air stream at

the edge of the working area in the room be ensured.

To increase the potential of indoor heat excess assimilation

by cool supply air the authors have designed a ventilation

system with local recirculation diffusers (Figure 2). This

system can supply lower temperature air (from +6 °C) into

the room to a local recirculation diffuser which mixes the

incoming outdoor air and the recirculation air from the room,

thus producing a supply air stream with comfort parameters

(temperature and air flow velocity) at the edge of the

working area in the room.

The operation of a recirculation diffuser (Figure 3) is

described below.

The low temperature outdoor air (≥ +6 °C) flows from the air

supply unit (not shown) into a pipe (4) and then is supplied

into the room via a diffuser (5). The diffuser (5) generates a

fan-shaped air stream which adheres to the ceiling. The

outdoor air flow rate remains constant for as long as the

system is in operation. A fan (7) feeds recirculation air (the

air from the serviced room) through a recirculation air pipe

(6) into the static pressure chamber (1); the air is cleaned as it

passes through a filter (8). Then, the clean air is directed into

the room by rows of eddying cells (3) on the face panel (2) of

the diffuser. The eddying cells (3) generate a fan-shaped

stream of recirculation air which adheres to the ceiling and

mixes with the outdoor air stream from the diffuser (5) thus

producing a supply air stream. A controller and a frequency

drive (not shown) control the speed of the fan (7) and the

recirculation air flow rate to maintain the supply air set

temperature.

The prospects for designing and using local recirculation

diffusers for energy-efficient ventilation systems are

substantiated in the work [11]. Computational modeling

research into the efficiency of the designed local

recirculation diffusers is described in the work [12]. This

article considers test results obtained for an experimental

installation of a local recirculation diffuser.



10723

Figure 3. Local recirculation diffuser design

METHODS

The experimental installation of a local recirculation diffuser

(LRD) (characteristics of the installation are given in

Table 1) was subjected to the following tests:

- aerodynamic tests of LRD;

- acoustic tests of LRD;

- tests of LRD in an office room.

Aerodynamic tests of a local recirculation diffuser were

carried out on an aerodynamic test bench at the

aerodynamics and acoustics research laboratory of LTD

“Arktos”, an industrial partner [13]. Figure 4 shows a

schematic view of an aerodynamic test bench for

aerodynamic tests of LRD.

Table 1: Main parameters and dimensions of the experimental installation of LRD

Main parameters and dimensions Values and units

Air purity class of the recirculation air filter F5

Dimensions of the recirculation air diffuser panel 450 × 450 mm

Dimensions of the static pressure chamber (H × W × D) 300 × 424 × 424 mm

Outdoor air pipe diameter 125 mm

Recirculation air pipe diameter 250 mm



10724

The objectives of aerodynamic tests were as follows:

- To determine the air drag of LRD in the outdoor air

and recirculation air circuits in order to choose the

fan to meet the characteristics of LRD;

- To determine the stream hydrodynamic coefficient

m;

- To determine the maximum ratio of the

recirculation air flow rate and the outdoor air flow

rate (the air output capacity) in order to verify the

conformity of the chosen fan to the stated

characteristics.

Aerodynamic tests were carried out in isothermal conditions

in accordance with national standards [14-15].

The tests involved the measurement of dynamic and total

pressure at measurement cross sections of the test sections

along the bench with a Kimo MP 200 thermo-anemo-meter

(France) fitted with a pressure probe (a Pitot tube).

Figure 4. A schematic view of an aerodynamic test bench for aerodynamic tests of LRD

The following parameters were calculated based on the

measurement results:

The air flow velocity in the test air ducts υ, m/s, and the flow

rate L, m3/h, given by the equations:

υ = √2Pdyn

ρ, (1)

L = 3600Fsect × υ, (2)

where: 𝑃dyn is the measured dynamic pressure, Pa;

ρ is the air density, kg/m3;

Fsect is the cross section area of the test section in the bench,

m2.

- The pressure loss coefficient for the diffuser was calculated

from:

=Pt

Pdyn, (3)



10725

Where 𝑃𝑡 is the total pressure; Pdyn is the dynamic pressure

defined based on the velocity in the air duct cross section: for

the recirculation air section Fsect= 0.049 m2; for the outdoor

air section of the diffuser Fsect= 0.0123 m2.

Characteristics of the adhering stream (velocity coefficient

m) were determined by the measurement of velocity fields at

cross sections of the generated supply air stream for different

distances Y from the axis of the air diffuser in the plane of

adherence. The air flow velocity measurements were taken

with a TTM-2 thermoanemometer system (EKSIS) and were

used to define the maximum air flow velocities, 𝜐𝑦𝑚𝑎𝑥, m/s, at

each cross section, and the velocity coefficient m. The latter

was calculated from:

𝑚 =𝜐𝑦

𝑚𝑎𝑥

𝜐0

·𝑦

√𝐹0

, (4)

where 𝐹0 = 0.303 𝑚2 (the cross section area of the static

pressure chamber).

As the result of the tests, the pressure loss coefficient for the

outdoor air circuit ζ = 7, the pressure loss coefficient for the

recirculation circuit (a non-constant value as the system

contains a filter, see Figure 5), and the hydrodynamic

coefficient m = 4.3 have been obtained. These results make it

possible to calculate pressure losses and stream

characteristics for any required air flow rate. The data

obtained for the recirculation air section allowed to select an

optimum fan which will ensure the required fun pressure at

low energy consumption.

Figure 5. A diagram of the pressure loss coefficient change for the recirculation air circuit based on the air flow velocity in the

recirculation air pipe

The results of the local recirculation diffuser aerodynamic

tests, as well as of the calculation of the characteristics for

two conditions, are set forth in Table 2.

y = 20.923x-0.568

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

14.0

15.0

16.0

17.0

18.0

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 V,m/s



10726

Table 2. Results of aerodynamic tests and LRD characteristics calculation

Item

No.

Parameter Values

Conditions 1 Conditions 2

1 Dynamic pressure at the measurement cross section of the recirculation air pipe test

section, Pa

4.4 0.33

2 Total pressure at the measurement cross section of the recirculation air pipe test

section, Pa

53 8

3 Actual air flow rate through the recirculation air pipe, m3/h 480 130

4 Pressure loss coefficient for recirculation air,

(F0 = Fsect = 0.149 𝑚2)

11.9 24.8

5 Dynamic pressure at the measurement cross section of the outdoor air pipe test

section, Pa

4.9 4.4

6 Total pressure at the measurement cross section of the outdoor air pipe test section,

Pa

34 33

7 Actual air flow rate through the outdoor air pipe, m3/h 127 125

8 Pressure loss coefficient for outdoor air,

(F0 = Ftestsect = 0.0123 𝑚2)

7.0 7.0

Acoustic tests of the local recirculation air diffuser were

performed on an acoustic bench of the aerodynamics and

acoustics research laboratory of LTD “Arktos”, an industrial

partner.

The acoustic tests performed on an acoustic bench were

aimed at determining the sound power levels emitted by the

local recirculation air diffuser when operated in the

conditions of simultaneous supply of outdoor and

recirculation air at the maximum capacity (at the

recirculation air flow rate of 480 m3/h).

In the process of testing, the universal multi-channel

multifunctional system “PULSE 3560-B-030”, equipped

with 5 microphone units, which contain 4189 type measuring

microphone and 2969L type pre-amplifier, was used. During

the measurements, UA 0459 type windbreaks were mounted

on the microphones. An end-to-end calibration of the test

vein with the help of 4231 type acoustic calibrator was

carried out before the commencement of measurements.

During the tests, the tested experimental installation of local

recirculation diffuser was installed via an adapter onto the air

supply unit of the process ventilation unit with a

continuously adjustable air flow rate in the center of the

anechoic room with a reverberating floor (Figure 6). The

measurement points were located on 2 m radius semi-sphere

with the measuring microphones’ scanning along five

circular paths in accordance with the requirements of

national standards [16-17]. The sound pressure levels were

averaged per each circular path. The parameters of the

circular paths are shown in Figure 7.

Besides, when LRD and the adapter distanced themselves at

each circular path, the levels of acoustic noise (noise

background) were determined for each air flow rate value.

Upon necessity, the measurement results were added with a

correction for the level of acoustic noises.

Figure 6. A picture of an anechoic chamber with a

reverberating floor

The levels of the sound power Lw emitted by the local

recirculation air diffuser were calculated using the following

equation:

Lw = Lpf + 10 lg (S/So) + C1 + C2, (5)

where Lpf is the mean level of sound pressure or the sound

level on the measurement surface:

Lpf = 10 lg (1/n · ∑ 100.1Lpini=1 ), (6)

where Lpi is the time-averaged sound level for i-th circular

path;

n is the number of circular paths (n=5);

S = 2πr2 is the measurement surface area, m2;

So = 1 m2;

C1 , C2 are the corrections for meteorological conditions

calculated in accordance with national standard [16].



10727

Figure 7. Five coaxial paths of measuring microphones

During the tests, the sound power levels (Lw) in dB, in 63,

125, 250, 500, 1000, 2000, 4000 and 8000 Hz octave bands,

and the corrected levels of sound power (LwA) in dBA,

emitted by the face panel of LRD, when operated in the air

supply conditions at the maximum value of recirculation air

flow rate (480 m3/h), were determined.

The results of acoustic tests are summarized in Table 3.

Table 3. Results of acoustic tests

Item

No.

Parameter Values

1 Actual air flow rate through the recirculation

air pipe, m3/h

480

2 Actual air flow rate through the outdoor air

pipe, m3/h

120

3 Time-averaged sound level for the i-th

circular path, dB

at point 1

at point 2

at point 3

at point 4

at point 5

47

49

50

51

48

4 Mean sound pressure level emitted by the

local recirculation air diffuser, dB

49

5 Total noise level generated by LRD, dB 54

The office room tests of a local recirculation air diffuser,

approximated to the truth, were performed on a specially

designed and mounted bench approximating office rooms

intended for four employees. The principal diagram of the

testing bench for an experimental installation of a

recirculation diffuser in office rooms is shown in Figures 8,

9.

The objective of these tests was the determination of the

dynamic characteristics of the control of recirculation air

diffusers, as well as the determination of microclimate

parameters (air temperature and velocity) in the working area

of the room with the aim to confirm the following:

- the volume of admixed recirculation air, based on

the outdoor air temperature (upon its change from 6

to 18 °C) and on the heat load in the room

(recirculation air temperature upon its change from

18 to 25 °C), for maintaining optimum comfort

parameters of the supply stream at the edge of the

working area in the room, is controlled

automatically;

- the compliance with service area microclimate

parameters regulated by the national standards of

the Russian Federation [18] is ensured.

Figure 8. The principal diagram of the testing bench for an

experimental installation of a recirculation air diffuser

During the tests, a constant outdoor air flow rate in the

volume of 240 m3/h (120 m3/h per each LRD) was supplied

from the supply unit. Due to the installed electric heater, the

supply (outdoor) air temperature was maintained at the level

not lower than +6 °C.

The supplied (outdoor) temperature and the recirculation air

temperature were determined by sensors. When the supply

air temperature lowered below +18 °C, the controller

calculated the recirculation air volume which had to be

supplied to LRD for heating the supply air. Based on the



10728

dependence of the air flow rate on the voltage, supplied to

the fan and determined at the aerodynamic bench, the

controller initiated a signal to the fan control.

A wattmeter was used to register the value of the electric

power consumed by the fan of the local recirculation air

diffuser.

In addition to air temperature and velocity, 2250

Bruel&Kjaer spectrum analyzer sound meter was used for

measuring sound levels in the working area of the room. The

measurement of microclimate parameters was carried out in

accordance with the methods described in the national

standard [18], for the presence of people in the room, mostly

in a sitting position, at the height of 0.1; 0.6 and 1.7 m from

the floor level.

According to the values set forth in Table 3 of the national

standard [18] for Category 2 rooms (rooms intended for

people engaged in intellectual pursuits or studies), the

optimum air temperature in cold season shall fall within the

range of 19-21 °C, while the optimum air flow velocity shall

not exceed 0.2 m/s.

Figure 9. Location of microclimate parameters measurement

points in the office room

The results of the tests performed in the office room are

summarized in Table 4.

Table 4. Results of the tests performed in the office room

Item

No.

Parameter Values

Conditions

1

Conditions

2

Conditions

3

1 Actual air flow rate

through the outdoor

air pipe, m3/h

127 125 126

2 Outdoor air

temperature, °C +6 +14.7 +20

3 Actual air flow rate

through the

recirculation air

pipe, m3/h

480 130 -

4 Recirculation air

temperature, °C +20.4 +21 -

5 Specific energy

consumption of

LRD fan, W/(m3/h)

0.13 0.11 -

6 Air temperature in

the working area of

the room, °C

19.2-19.5 20.0-20.3 21.0-21.4

7 Air flow velocity in

the working area of

the room, m/s

< 0.19 < 0.1 < 0.1

8 Level of noise

generated by the

recirculation air

diffuser, dBA

43.9-46.4 39.9-40.4 < 35

DISCUSSION

Based on the performed tests of an experimental installation

of a local recirculation air diffuser it was concluded that:

1) The designed LRD system ensures the recirculation air

and outdoor air ratio (4:1) (the necessity of maintaining

the stated ratio value is substantiated in work [11]).

2) The air drag at the outdoor and recirculation air circuits

has a low value, which ensures low demand for electric

power for supplying outdoor air to the working area of

the room;

3) The review of the obtained the acoustic test results

shows that, at the distance of 3.5 m, within the area of

the sound direct impact, the sound pressure level

generated by the local recirculation air diffuser will

come to 45 dB(A) which complies with the requirements

of Russian standard [19] for any types of workplaces of

administration rooms; and at the distance of 5 m, within

the area of direct sound impact, the sound pressure level

generated by the local recirculation air diffuser will

come to 40 dB(A).

Supplementary research has shown that the main

contribution to the total noise exposure, created by the

local recirculation air diffuser, is made by the fan, and

that the total sound level in dBA is determined by the

acoustic radiation at the fan blade passage frequency.

This fact has determined the replacement of the fan built

into the local recirculation air diffuser, which made it



10729

possible to ensure the sound pressure level generated by

the air diffuser of below 40dB(A) at the distance of 2-2.5

m.

4) The tests performed in the office rooms have confirmed

automatic obtainment of comfort microclimate

parameters in cold and transitional seasons in the

working area of the room (air temperature and velocity,

sound pressure) regulated by the national standard [18],

in case of using ventilation systems with local

recirculation air diffuser in the conditions of the

changing temperature of outdoor air supplied to LRD, as

well as the changing recirculation air temperature (due

to the change of the heat load in the room).

CONCLUSION

The performed tests have confirmed the assurance of

comfortable air-heat parameters in the room serviced by the

ventilation system with local recirculation air diffusers.

For further investigation and use of the designed ventilation

system with a local recirculation air diffuser, a pilot project

of the considered system for office rooms shall be developed.

This project shall be afterwards implemented and the

installed ventilation system with local recirculation air

diffusers shall be audited with the aim to identify the

following:

- actual energy efficiency of the system in real

conditions;

- actual employees’ satisfaction with the air-heat and

acoustic comfort maintained by the system in the

rooms.

ACKNOWLEDGEMENTS

This research was supported by the Ministry of Education

and Science of the Russian Federation under the federal

target program “Research and Development on Priority

Directions of the Research and Technological Complex of

Russia in the Years 2014-2020” (Grant Agreement No.

14.576.21.0037 dated 27 June 2014, Unique Identifier

RFMEFI57614X0037).

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10730

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