Emission effects of three different ventilation control strategies—A scale model study

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B I O S Y S T E M S E N G I N E E R I N G 1 0 0 ( 2 0 0 8 ) 9 6 – 1 0 4

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Research Paper: SE—Structures and Environment

Emission effects of three different ventilation controlstrategies—A scale model study

G. Zhanga,�, B. Bjergb, J.S. Strøma, S. Morsinga, P. Kaia, G. Tongc, P. Ravna

aInstitute of Agricultural Engineering, Aarhus University, DenmarkbInstitute of Large Animal Sciences, Copenhagen University, DenmarkcCollege of Water Conservancy, Shenyang Agricultural University, China

a r t i c l e i n f o

Article history:

Received 15 May 2007

Received in revised form

25 January 2008

Accepted 5 February 2008

Available online 2 April 2008

nt matter & 2008 IAgrE.emseng.2008.01.012

hor. Tel.: +45 [email protected]

The objectives of this paper are to determine the effects of varying the ventilation rates on

ammonia emission using three different control strategies: constant inlet opening area,

constant inlet air velocity and constant inlet air jet momentum. In addition, methods for

estimation of air exchange rates between the headspace and the room are investigated.

The work is based on scale model experiments in three different floor configurations.

The model was made to scale 1:12.5 of a sub-section of a pig house with double rows of

pens. Ventilation air was supplied through adjustable slats at two sides beneath the ceiling

spanning the whole width of the model. Ammonia water was added in the scale model

bottom to serve as a reservoir providing measurable gas emission. In addition to no-floor,

two types of slatted floor were investigated with opening area 33.3% and 16.7%.

The effect on the emission of increasing the ventilation rate is seen to greatly depend on

the control strategy. The highest emission rate was found for constant inlet opening. The

emission was reduced considerably when the inlet opening was adjusted to maintain

constant inlet velocity, and when the inlet opening was adjusted to maintain constant

momentum the emission was nearly independent of ventilation rate. The maximum

emission was found with no slatted floor and the minimum emission was found for the

slatted floor with the lower opening area.

& 2008 IAgrE. Published by Elsevier Ltd. All rights reserved.

1. Introduction

Exhaust ventilation air from livestock production buildings is

a major source of pollution to the environment from agri-

cultural operation. Indoor air quality in the building affects

the well-being of both animals and workers.

In many cases, it is concluded that the ammonia emission

rates from a livestock building are dependent on the

ventilation rates and the higher the ventilation rates, the

higher the emission (Aarnink et al., 1995; Topp et al., 2001;

Zhang et al., 2005). However, there is little in the literature on

Published by Elsevier Ltdk (G. Zhang).

the magnitude of these effects. Besides, there is very limited

knowledge on the estimation of the air exchange rate in

slurry pits in ventilated livestock buildings, even though this

knowledge is crucial for emission estimation and reduction

from a building (Sommer et al., 2006).

The effect of different airflow patterns created by floor type

and slurry channel layout on ammonia emissions has been

reported by Morsing et al. (2008). The objectives of this

investigation are focused on the effects of varying the

ventilation rate under three different control strategies:

constant inlet openings, constant inlet velocity and constant

. All rights reserved.

dx.doi.org/10.1016/j.biosystemseng.2008.01.012

mailto:[email protected]

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Nomenclature

Ao inlet opening area, m2

C ammonia concentration, mg m�3

Cd coefficient of discharge

d diameter of orifice, m

E emission rate, mg s�1

Io inlet air momentum, kg m s�2

L ventilation airflow rate, m3 s�1

m mass of inlet air per second, m ¼ rvoAo, kg s�1

Rflop floor opening ratio, Rflop ¼ floor opening area/total

floor area, dimensionless

Vpit air exchange rate in pit, m3 s�1

v air velocity, m s�1

vo inlet air velocity, m s�1

b diameter ratio (diameter of the orifice/diameter of

the vent pipe)

DE variation of emission rate, mg s�1

Dp pressure drop over the slatted floor, Pa

DP pressure difference between the upstream side

and the downstream side of the orifice, Pa

r density of air, kg m�3

Subscript

ex exhaust

inlet inlet

NH3 ammonia

pit pit

room room

B I O S Y S T E M S E N G I N E E R I N G 1 0 0 ( 2 0 0 8 ) 9 6 – 1 0 4 97

inlet air jet momentum. In addition, the methods for

estimation of air exchange rates between the headspace

and the room are investigated. The work is based on scale

model experiments in three different floor configurations.

2. Materials and methods

2.1. Experiment model

2.1.1. Experiment scale modelThe scale model was made as a sub-section of a pig house

with double rows of pens 4.8 m wide and 2.4 m wide with a

Fig. 1 – Dimensions (cm) of a full-scale pig h

Gyl

le18

0190155

500

155 50

70

Slur

ry 1

80190155

500

155 50

70

Gyl

le18

0190155

500

155 50

70

Slur

ry 1

80190

500

155

50

70

155

Fig. 2 – Dimensions (mm) of the 1:12.5-scale pi

1.0 m inspection alley in between. The partitions were

assumed to be solid and 0.875 m high. The ceiling height

from the floor surface was assumed to be 2.6 m. The slurry pit

was assumed to be 1.20 m deep with 0.6 m headspace above

the manure surface (Fig. 1).

The model was made to scale 1:12.5. It was 500 mm wide,

840 mm long and 450 mm high. The ceiling height measured

from the floor surface was 210 mm. The inspection alley and

the partitions spanned the full width of the model (Fig. 2). The

partitions were 70 mm high.

Ventilation air was supplied through adjustable slats on two

sides beneath the ceiling spanning the whole width of the

model. The maximum opening height of each inlet was

ouse section with double rows of pens.

450

D 35

840 130

100

80

90

380380

4510

165

840 130

100

80

90

380380

4510

165

840 130

100

80

90

380380

4510

165

840 130

100

80

90

380

4510

380

165

g house section with double rows of pens.

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Fig. 3 – Connections between scale model ammonia

reservoir and the storage tank.

Table 1 – Control strategies used in the experiments

Control strategies Inlet opening

height (m)

Ventilation

rate (m3 s�1)

Constant inlet opening 0.005 0.005

0.005 0.010

0.005 0.015

0.005 0.020

Constant inlet velocity 0.005 0.005

0.010 0.010

0.015 0.015

0.020 0.020

Constant inlet jet momentum 0.005 0.005

0.020 0.010

0.045 0.015


45 mm. Room air was exhausted near the ceiling in the centre

of the model through a clear acrylic pipe, 35 mm in diameter,

extending 38 mm downwards from the ceiling. The pipe was

connected via a flexible duct to a Lindab-type QBU100D

channel fan discharging the air to the outside.

Below the floor a 230 mm deep slurry pit was made.

Ammonia water was to be added to a depth of 160 mm to

serve as a reservoir providing measurable gas emission.

Except for the depth of the slurry channel, the dimension of

the scale model was thus close to 1:12.5 of the full-scale room.

2.1.2. Ammonia waterAmmonia water was circulated from a 50 l storage tank to

the slurry pit in the bottom of the scale model with a

Heissner type PA1000 garden pump through a 6-mm-diameter

rubber hose. The liquid was drained back by an overflow pipe

to the storage tank, leaving a 160-mm-deep reservoir of

ammonia water in the bottom of the scale model. This gave a

70 mm headspace between the water surface and the floor

(Fig. 3). Provision was made for enough ammonia to be

available for prolonged evaporation and minimized reduction

of ammonia concentration in the source liquid during the

experiments.

The ammonia water was made of two mixtures in tap

water. The first mixture was an ammonium chloride (NH4Cl)

solution to function as the ammonia source. The second

mixture was buffer solution made with sodium carbonate

(Na2CO3) and sodium hydrogen carbonate (NaHCO3). A

target pH value of 8.3 in the ammonia water was used to

maintain a robust balance between ammonium and ammo-

nia in the water with enough ammonia available for

evaporation.

2.1.3. Floor typesThree slatted floor types were investigated with various

opening areas: 100%, 33.3% and 16.7%. The 100% opening

area meant that the headspace was an integral part of the

room air space and this configuration was used as the

reference treatment.

The slats for the fully slatted floor were 5.3 mm (70.1 mm)

wide and 10 mm deep with 3 mm (70.1 mm) slots between.

The opening area was 33.3% with all slats open and 16.7%

with every second slat sealed off with tape. The slurry

channel sides extended from the underside of the floor

well into the ammonia water so that the air space below the

pens was sealed off from the neighbouring parallel pens.

The designed pen dimension of 380 mm�190 mm, placed in

the middle of the scale model, left 155 mm space to the

sidewalls.

2.2. Experimental set-up

2.2.1. Ventilation control strategiesThe experiments were conducted in four different ventilation

airflow rates with three control strategies, namely fixed inlet

opening area, inlet area adjusted to maintain constant supply

velocity and inlet area adjusted to maintain constant inlet

momentum, as described in Table 1.

2.2.2. Experimental seriesThree measurement series were carried out during the

experiment:

Series 1: no slatted floor (100% opening area) with

inspection alley partitions.

Series 2: slatted floor with 33.3% opening and inspection

alley partitions.

Series 3: slatted floor with 16.7% opening and inspection

partitions with solid floor.

2.3. Measurement

Experiments were carried out in Air Physics Lab, Research

Centre Bygholm, Faculty of Agricultural Sciences (formally

Danish Institute of Agricultural Sciences), University of

Aarhus, Denmark.

2.3.1. Ventilation airflow rates and inlet air velocitiesOrifice plates designed according to ISO 5167-1 were

applied to measure the ventilation airflow rates. Airflow rate

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Table 2 – Measurement positions of the ammonia concentration

Instrumentchannels

Test series 1 Test series 2 Test series 3

A In the exhaust channel 140 mm from the outlet At the same position as Test 1 At the same

position as Test 1

B In the centre of the model and 50 mm below the

floor level

In the centre of the model and 50 mm above

the floor

The same as in

Test 2

C Under the floor and 210 mm from the left sidewall;

10 mm above liquid surface

Under the floor and 50 mm from the right

sidewall; 10 mm above liquid surface

At the same

position as in

Test 2

D Under the floor and 210 mm from the right sidewall;

10 mm above liquid surface

At the same position as in Test 1 At the same

position as in

Test 1


is related to the measured differential pressure and may be

determined by

L ¼Cdffiffiffiffiffiffiffiffiffiffiffiffiffiffi

1� b4q p

4d2

ffiffiffiffiffiffiffiffiffi2DPr

s(1)

where L is the airflow rate, m3 s�1; Cd is the coefficient of

discharge; b is the diameter ratio (diameter of the orifice/

diameter of the vent pipe); r is the density of air, kg m�3; d is

the diameter of orifice, m; and DP is the pressure difference

between the upstream side and the downstream side of the

orifice.

The differential pressures were measured by an FC0510

Micromanometer (Furness Controls Ltd., England) with a

measurement range of 0–2000 Pa, and an accuracy of 70.3%

and a resolution of 0.01 Pa. The data were recorded during the

experiments with a sampling period of 1 s.

The inlet velocities were obtained based on the ventilation

airflow rates and the inlet opening area. During the experi-

ments, the inlet air velocities were also checked at the

middle position of the inlet height with a Testo 400 (Testo

GmbH & Co., Germany) velocity sensor. The sensor has a

measurement range of 0–20 m s�1 and an accuracy of 70.01

m s�1 (0–1.99 m s�1), 70.02 m s�1 (2–4.9 m s�1) and 70.04 m s�1

(5–20 m s�1) and a resolution of 70.01 m s�1 (0–20 m s�1).

Smoke was used in the experiments to indicate the direction

of local airflow to provide a quick visualization of the path of

the airstreams and pressure differentials.

2.3.2. Ammonia measurementAmmonia concentrations were measured at the exhaust, near

the inspection alley and under the floor with a 1312

Photoacoustic Multi-gas Monitor and a multiplexer 1303

(Innova Air Tech Instruments A/S, Denmark). Four measure-

ment channels were used: Channel A was used to measure

the concentration in the exhaust air and Channel D was used

to measure the concentration in the headspace near the

sidewall; the measurement positions for Channels C and D

were varied in the experiments to check the variations of the

concentration in the room and slurry headspace. Details of

the measurement positions are listed in Table 2. For each

experimental run, the data were sampled for 90 min. The

sampling period for each measurement was 20 s, followed by

20 s cleaning time to replace the air in the measuring

chamber of the instrument before a new measurement

channel was started.

2.3.3. Computation of ammonia emission rateThe ammonia emission rates from the ventilated model

space were calculated based on the ventilation rate, ammonia

concentrations at exhaust unit and outside:

ENH3 ;room ¼ LðCex � CinletÞ (2)

where L is the ventilation rate, computed in Eq. (1) based on

the measured differential pressure, m3 s�1; Cex is the ammo-

nia concentration in exhaust air; and Cinlet is the ammonia

concentration at inlet. In this study, the inlet ammonia

concentration was assumed to be zero.

3. Result and discussion

3.1. Air exchange rates in the headspace of the slurry pit

Since there was no emission source on the floor, the total

emission from the model envelope was from the ammonia

water surface. Accordingly, the air exchange rates of head-

space in the slurry pit were estimated using the concentration

differences between the slurry pit and the air space above the

floor, i.e.,

ENH3 ;room ¼ ENH3 ;pit ¼ VpitðCroom � CpitÞ (3)

Data from channel D were used as the concentration in pit,

Cpit, and the concentrations in the exhaust air measured in

channel A were used to represent the average concentration

in room, Croom. It should be mentioned that using the

concentration in the exhaust air as the average concentration

in a ventilated room may depend on the airflow pattern and

mixing in the room space. To check the uncertainty of the

assumption, the concentrations measured at the exhaust

were compared with the measured values in the middle of the

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0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0

Air

exc

hang

e ra

te, m

3 s-1

0.05 0.1 0.15 0.2

Inlet air momentum, kg m s-2

Fig. 4 – Air exchange rates in the slurry channel varied

following inlet air momentum, & and —, measured values

and modelling results for 33.3% floor opening; n and ,

measured values and modelling results for 16.7% floor

opening.


model and at 50 mm under the floor level in test series 1. The

results are presented and discussed in Section 3.3.

The estimated air exchange rates are shown in Fig. 4. In a

ventilated pig building with slatted floor without slurry pit

ventilation, the air change rate in the slurry pit is influenced

by room ventilation conditions and slatted floor opening ratio.

The floor opening ratio is defined as the ratio of floor opening

area to the total floor area expressed as a percentage. In a

ventilated room space, openings of floor slots function as

both air inlets and outlets for the headspace of the slurry pit.

Which parts of the openings are active as inlets or outlets at

any time depends on the airflow patterns and air velocity

above the slatted floor. The airflow pattern and air velocities

at the floor level were directly related to the room inlet air

momentum. Higher air velocity above the floor and higher

floor opening ratio will result in higher air exchange rate of

the slurry pit. According to the results, a correlation between

air exchange rate of the headspace in a slurry pit and inlet air

momentum may be established

Vpit ¼ 0:683I0:77o R0:41

flop (4)

with R2 of 0.97, where Vpit is the air exchange rate in pit,

m3 s�1; Io is inlet air momentum, kg m s�2; and Rflop is floor

opening ratio in percent. With 95% confidence intervals, the

standard errors for the model parameters a ¼ 0.683, b ¼ 0.77

and c ¼ 0.41 are 0.0198, 0.074 and 0.166, respectively.

It should be mentioned that this was only a primary

investigation based on a scale model and only two floor

opening ratios were applied. This correlation, however, needs

to be validated in a full-scale building with different floor

opening ratios. Further investigations and modification for

the model are needed for different ventilation systems and

indoor partitions.

3.2. Control strategy for ventilation airflow rate tominimize emission

The measurement results of the emissions under different

control strategies are presented in Fig. 5.

3.2.1. Effect of control strategyIn the experiments a ventilation rate of 0.005 m3 s�1 was

used as the reference situation. The effect on the emission of

higher ventilation rates is seen to be greatly dependent on the

control strategy. The highest emission rate was found for

constant inlet opening. The emission was reduced consider-

ably when the inlet opening was adjusted to maintain

constant inlet velocity, and when the inlet opening was

adjusted to maintain constant momentum the emission was

nearly independent of ventilation rate.

The effect of the control strategy may be explained by the

airflow dynamics in the boundary layer of the emission

surface and the gas transport in the building spaces. Without

any floor, the room ventilation air was in direct contact

with the whole emitting surface. With the constant inlet

opening strategy the inlet air velocity increases as ventilation

rate increases. This resulted in a higher air velocity at the

emission surface. A linear correlation between inlet air

velocity and floor air velocity in a full-scale room has been

found by Strøm et al. (2002). The increased air velocity at the

emission surface may explain the increased emission rate of

ammonia. This is in accordance with Arogo et al. (1999); Topp

et al. ( 2001) and Zhang et al. (2005) who have reported that

the higher the air velocity is at an emission surface, the

higher the emission rate will be.

Accordingly, with the constant inlet air velocity strategy,

increased ventilation rate increased the inlet air momentum

and decreased the ammonia concentration in the room air

space. However, variations of the air velocity at the emission

surface were very limited due to the constant inlet air velocity

according to the jet flow decay theory.

With the constant inlet air momentum strategy, the higher

ventilation rate will result in a lower inlet air velocity and

consequently a lower air velocity at emission surface. The

size of the inlet opening rapidly becomes a limiting factor

when compensating for a higher ventilation rate, however.

3.2.2. Effect of slatted floorIn test series 2 and 3, a slatted floor with 33.6% and 16.7%

opening was installed above the emitting surface. According

to the jet decay theory, the air velocity at the floor level would

vary as a function of the inlet air velocity, but the presence of

the floor will affect the air exchange rates in the headspace of

the slurry pit under the slatted floor.

As expected, the maximum emission was found in the

reference case without slatted floor and the minimum

emission was found for the slatted floor with the lower

opening area. In all the three cases the use of the constant

momentum strategy provided decreased emission rates.

3.2.3. Modelling of the emission ratesUsing nonlinear model fitting, the emission rate can be

described as a function of inlet velocity, inlet opening area

and slatted floor opening ratio:

ENH3 ¼ 1:62v0:73o A0:46

o R0:38flop (5)

with R2 of 0.98 based on the measured data, where ENH3is

ammonia emission rate, mg s�1; vo is inlet air velocity, m s�1;

Ao is inlet opening area, m2; and Rflop is floor opening ratio.

The curves based on the model in Eq. (5) are presented in

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0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0

Ventilation rate, m3s-1

Am

mon

ia e

mis

sion

, mg

s-1

0

0.05

0.1

0.15

0.2

0.25

0.3

Ventilation rate, m3 s-1

Am

mon

ia e

mis

sion

, mg

s-1

0.00

0.05

0.10

0.15

0.20

0.25

Am

mon

ia e

mis

sion

, mg

s-1

0.005 0.01 0.015 0.02 0.025 0 0.005 0.01 0.015 0.02 0.025

Ventilation rate, m3 s-1

0 0.005 0.01 0.015 0.02 0.025

(a) (b)

(c)

Fig. 5 – Ammonia emission versus ventilation airflow rate: (a) without floor; (b) with 33.6% floor opening; and (c) with 16.7%

floor opening: where B and - - -, � and —, n and represent the results of the measurements and the estimated model by

using constant inlet opening, constant inlet velocity and constant inlet air momentum, respectively.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0

Inlet air momentum, kg m s-2

Am

mon

ia e

mis

sion

, mg

s-1

0.05 0.1 0.15 0.2

Fig. 6 – Emission rates as a function of inlet air momentum

and floor opening ratio: B and - - -, without floor; & and —,

with 33.6% floor opening; n and , 16.7% floor opening

represent the measured and the modelled values,

respectively.


Fig. 5 to compare with the result of the measurements. With

95% confidence intervals, the standard errors for the model

parameters a ¼ 1.62, b ¼ 0.73, c ¼ 0.46 and d ¼ 0.38 are 0.387,

0.053, 0.055 and 0.032, respectively.

Since the inlet air momentum can be expressed as

Io ¼ mv ¼ rAov2o (6)

an alternative version of the emission model based on inlet

air momentum and opening ration of slatted floor is

ENH3 ¼ 0:69I0:36o R0:39

flop (7)

with R2 of 0.95 based on the measured data. With 95%

confidence intervals, the standard errors for the model

parameters a ¼ 0.69, b ¼ 0.36 and c ¼ 0.39 are 0.089, 0.031

and 0.046, respectively.

The measured emission data and modelling curves as

function of inlet air momentum and floor opening ratio are

shown in Fig. 6. A sensitivity analysis (Table 3) of the

variations of ammonia emission related to variations of inlet

air momentum and floor opening ratios was performed for

this model (Eq. (7)). The sensitivity measure used was the

normalized response given by Isukapalli (1999). Based on the

analysis results, the emission rate is more sensitive to

momentum variation at a lower momentum for a given

floor opening ratio than at high momentum. Similarly, the

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Table 3 – Sensitivity analysis values for the emission model, Eq. (7)

Floor

opening

ratio (%)

Inlet air momentum

(kg m s�2)

Sensitivity ¼ |DE/E|

(%)

Inlet air

momentum

(kg m s�2)

Floor opening ratio Sensitivity ¼ |DE/E|

(%)

Initial Io Io7DIo (DI ¼ 0.005) Initial Rflop (%) Rflop7DRflop (DRflop ¼ 1%) (%)

100 0.05 0.045 3.37 0.05 30 31 1.29

0.055 3.15 29 1.31

0.1 0.095 2.96 20 21 1.92

0.105 2.86 19 1.98

0.15 0.145 1.96 10 11 3.78

0.155 1.92 9 4.02

33.3 0.05 0.045 3.37 0.1 30 31 1.29

0.055 3.15 29 1.31

0.1 0.095 1.66 20 21 1.92

0.105 1.60 19 1.98

0.15 0.145 1.10 10 11 3.78

0.155 1.92 9 4.02

16.7 0.05 0.045 3.37 0.15 30 31 1.29

0.055 3.15 29 1.31

0.1 0.095 1.66 20 21 1.92

0.105 1.60 19 1.98

0.15 0.145 1.10 10 11 3.78

0.155 1.07 9 4.02

Table 4 – Concentration at two symmetric positions above the surface of ammonia water (test series 1)

Control strategies Ventilationrate (m s�1)

Concentration atChannel C (mg m�3)

Concentration atChannel D (mg m�3)

Relative differenceDC=C̄ a (%)

Mean STD Mean STD

Constant inlet opening 0.005 66.7 6.5 67.1 9.5 0.7

0.010 54.6 2.8 52.4 3.7 4.2

0.015 49.5 3.8 44.2 2.6 11.4

0.020 43.3 3.5 39.1 1.2 10.3

Constant inlet velocity 0.005 60.2 8.3 55.9 6.3 7.5

0.010 48.7 2.6 51.7 4.1 5.9

0.015 47.0 4.6 45.8 3.5 2.7

0.020 46.1 3.3 43.9 5.0 4.8

Constant inlet jet momentum 0.005 56.8 4.5 56.1 3.5 1.2

0.010 55.3 7.1 73.7 8.2 28.5

0.015 34.0 7.6 40.2 3.9 16.6

a DC is the difference between the two means from the two channels and C̄ is the average of the two means.


variation of ammonia emission is greater at the lower floor

opening following a variation of the floor opening ratio.

In an individual building, the Rflop is a constant and the

emission from the slurry pit will only depend on the inlet air

momentum. Therefore, when controlling the ventilation

system, rapid increases in ammonia loss would be avoided

by maintaining air momentum at a low level.

3.3. Variations of ammonia concentrations

In a ventilated air space, the fresh air and room air are

incompletely mixed before the air is exhausted via the outlet.

Table 4 shows the concentration data at two symmetric

positions of the model, 210 mm from the sidewalls and

10 mm above the liquid surface. The relative differences of

the concentrations at the two positions are generally less

than 10%. The largest differences were found with the

constant momentum and the increased inlet openings.

These results indirectly indicate that the ventilation system

with two sidewall inlets and an exhaust unit at middle

of the ceiling created symmetric airflow patterns in

the model. Therefore, only the measurement position via

Channel D was used unchanged for the rest of the

experiments.

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Table 5 – Concentrations at exhaust and in the centre of the model below the floor level (test series 1)


Concentration atChannel A (mg m�3)

Concentration atChannel B (mg m�3)


Mean STD Mean STD


0.010 24.5 1.0 23.3 0.2 5.4

0.015 20.5 0.2 19.8 0.7 3.5

0.020 18.3 0.6 17.7 1.3 3.7


0.010 21.0 0.7 18.6 0.3 12.5

0.015 15.7 0.2 13.3 0.8 16.5

0.020 13.2 0.3 10.6 0.4 21.6


0.010 15.6 1.0 14.9 4.2 4.7

0.015 11.9 0.4 15.7 2.3 27.8

a DC is the difference between the two means from the two channels and C̄ is the average.

Table 6 – Concentration at two positions in the headspace of the slurry pit (test series 3)


Concentration atChannel C (mg m�3)

Concentration atChannel D (mg m�3)


Mean STD Mean STD


0.010 81.9 8.9 61.1 3.7 29.2

0.015 59.3 3.7 53.6 5.1 10.2

0.020 49.1 3.6 45.6 0.7 7.5


0.010 85.7 2.0 85.0 4.2 0.8

0.015 103.4 12.2 84.0 9.9 20.7

0.020 75.4 12.8 73.7 4.8 2.2


0.010 146.2 3.7 93.8 36.5 43.7

0.015 122.8 2.9 74.9 13.7 48.4

a DC is the difference between the two means from the two channels and C̄ is the average.


The measured concentration data at the exhaust and in the

middle of the model below the floor level are presented in

Table 5. The measured values in the two positions were

similar, which again suggests that there were two symmetric

airflow patterns on each side of the room space. The airflow

patterns were controlled by the inlet air momentum and the

mixed room air from the two sides met in the middle of the

room and then travelled downwards to the floor and slurry

surface. It also indicates that near the main downwards

stream, the concentration levels were the same and therefore

less variation was found between measured values at the

exhaust and at the end of the downward flow.

A set of measured concentrations at two different positions

in the slurry pit is given in Table 6. It can be seen that, in

general, the concentration values at a position near a side-

wall, Channel C, were rather higher than those measured in

the middle of one side-section in the headspace, Channel D.

The explanation may be that, following the airflow eddy

patterns, the room air mainly entered the pit headspace at

the floor opening near the centre of the room, and travelled

parallel to the liquid surface and returned to the room at the

floor opening near the sidewalls.

4. Conclusions

The effect of increased ventilation rate on ammonia emission

is dependent on the control strategy. The greatest increase in

emission rate was found for constant inlet opening. The

emission was reduced considerably when the inlet opening

was adjusted to maintain constant inlet velocity, and when

the inlet opening was adjusted to maintain constant mo-

mentum, the emission was nearly independent of ventilation

rate.

ARTICLE IN PRESS


Air exchange rate in and ammonia emission from the slurry

pit can be described as functions of inlet air momentum and

floor opening ratio. Increasing inlet air momentum and floor

opening ratio will result in higher air exchange rate in and

ammonia loss from the slurry pit. Increasing ventilation rate

by maintaining a constant inlet momentum may be used to

minimize any increase in the emission rate.

These findings, however, need to be validated in full-scale

buildings with different floor opening ratios. Further investiga-

tions on the effects of different ventilation systems and indoor

partitions on those correlations should also be considered.

Acknowledgements

The research was performed as part of the ROSES project

‘‘Reduction of Odour Source in and Emission from Swine

Buildings’’ under the Program ‘‘Animal Husbandry, the

Neighbours and the Environment’’ funded by the Danish

Ministry of Food, Agriculture and Fisheries (Grant Number:

3304-VMP-05-032-01).

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Emission effects of three different ventilation control strategies—A scale model study

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