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Defra project AC0123
Appendix 3
Mechanical versus natural ventilation for dairy cows
The aim of this chapter is to provide a plausible answer to the question whether or not
emissions from naturally ventilated buildings significantly differ from emissions from
mechanically ventilated buildings. Dairy cows are taken as the starting point but outcomes
are possibly also valid for other livestock categories.
1 Model approach
Ammonia emission is influenced by many factors like feed composition (protein content and digestibility), pH, urease activity, amount of emitting area, temperature, air velocity,
management, slurry composition etc. Most of these factors are not influenced by the
ventilation system but a ventilation system has a direct effect on ventilation rates and
therefore on inside air temperature and air velocity over the emitting surface areas. It is
assumed that mechanically ventilated houses have lower ventilation rates than naturally
ventilated houses where wind speed and direction have more influence. The greater
ventilation rates (increasing ammonia emission) result in lower inside air temperatures
(decreasing ammonia emission). Ventilation rates are calculated based on CIGR equations
(CIGR, 2002) and (Mosquera et al., 2010). Inside temperatures can be calculated with the
ANIPRO model (Ouwerkerk, 1999) that is also based on the CIGR calculations for heat
production and CO2 production. The ammonia emission can be calculated with the Ammonia
Emission Model Version 2.0. This model is based on Monteny et al. (1998). The hypothesis
is that differences in emission between naturally and mechanically ventilated houses are
mainly caused by differences in air temperature and air velocity given the same animal- and
manure management. So, with the models we can approach differences in ammonia
emission through the calculated differences in temperature, ventilation rate and using the
dimensions of the house, the air velocity over the emitting surface area.
As input for both models a standardized cubicle house for 100 dairy cows was chosen in the
2+2 design (meaning 2 outer rows and 2 inner rows of cubicles of both sides of a central
feeding lane) with the following dimensions (Table 1).
Table 1
Dimensions of standardized dairy facility for 100 cows.
Cubicle width
# cubicles outer rows
# cubicles inner rows
Width walking alley 1/4
Width walking alley 2/3
Width feeding lane
Length cubicles outer rows
Length cubicles inner rows
Gutter height
Roof slope
Ridge height
Height difference gutter-ridge
1.15
28
22
2.5
3.5
6
2.7
2.4
2.0
20
7.1
5.1
m
m
m
m
m
m
m
o
m
m
1
Total length
Total width
Total area (gross)
Total walking (emitting) area
Total lying area
Total volume
Roof area
Cross section
32.2
28.2
908.0
420.0
295.3
4146
966.3
128.8
m
m
m2
m2
m2
m3
m2
m2
The bodyweight of the cows was taken to be 600 kg, milk production was 25 kg milk per day
and the cows were 50 days in-calf. The total heat production is assumed to be similar to the
heat production of a practical herd.
The roof was assumed to be made of non-insulated roof panels, side walls are completely
open, end walls are closed. Slurry storage is situated underneath the slatted floors in the
walking alleys. The concrete slatted floors have slats with a width of 3.5 cm and the beam
width is 12.8 cm.
Table 2 presents the default input parameters of the Ammonia Emission Model.
Table 2
Starting input parameters of the Ammonia Emission Model.
Animals
# Cows
Urination frequency
Urea concentration
N-content slurry
100
10
7.50
3.06
Pasturing
Integration period
Runs
0
30
10
/day
g-N/l
g-N/l
days
days
Floor
Area
Temperature
Air velocity
Urine puddle
-size
-thickness
pH
420
10
0.2
m2
1
0.5
8.5
m2
mm
°C
m/s
Pits
Area
Temperature
Air velocity
pH
420
10
0.05
8.50
2 Effect of temperature
The effect of temperature on emission, as calculated by the Ammonia Emission Model is
shown in table 4. Van Duinkerken et al (2003) report a temperature effect of 2.75% per
degree Celsius.
Table 3
Ammonia emission of the house in g/h at different inside temperatures
Temperature
0
5
10
15
20
25
30
Emission NH3
[g/h]
121.7
146.8
172.6
193.0
207.5
217.3
227.2
Emission change
∆T=5
∆T=10
21%
18%
12%
8%
5%
5%
42%
31%
20%
13%
9%
3 Effect of air velocity
Effect of air velocity at floor level or in pits is shown in tables 5 and 6. In the Ammonia
Emission Model the effect of velocity in pits is linear and independent from the emission
effect of air velocity at floor lever.
2
m2
°C
m/s
Table 4
Emission of the house at different air velocities
Air velocity in pits
[m/s]
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
Emission
NH3
[g/h]
155.4
166.3
175.0
183.4
193.0
201.4
208.6
215.8
222.8
231.6
Air velocity at floor
[m/s]
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
Emission
NH3
[g/h]
148.9
173.2
183.4
193.0
198.6
201.2
204.4
207.0
208.2
211.7
4 Differences in ventilation rates for natural and mechanical ventilation
The goal of ventilation is the removal of heat, moisture and gasses (CO2, NH3, CH4, H2S etc.)
from the building. CIGR equations take total heat production, CO2 production and CO2
concentration and animal activity to calculate the ventilation rate in m3 per hour. Minimum
ventilation rates roughly range from 200 to 500 m3/hour per cow with CO2 concentrations of
600 and 350 ppm for indoor and outdoor conditions respectively.
Table 5
Calculated
Body Mass
[kg]
600
700
Milk production
[kg/day[
25
50
DIC
[days]
50
170
Minimum ventilation
[m3/hour]
211
525
Beside sensitive heat production, solar radiation, the insulation values of building materials
etc., play a role in the heat balance of the building and the resulting temperature at a given
ventilation rate. ANIPRO uses these factors to calculate the inside temperature for a naturally
ventilated building using only thermal buoyance as the driving force behind.
Table 6
Calculated inside temperatures based in minimal required ventilations raters
Outside temperature
[oC]
10
15
20
25
Inside temperature
[oC]
14.8
19.5
24.0
28.3
Assuming the mechanically ventilated buildings' ventilations rates are close to minimal
requirement, inside temperatures are about 4 oC higher than outside temperatures.
Ventilation rates in naturally ventilated animal houses were measured by Mosquera et al.
(2011) and ranged from around 500 m3 per hour per animal to more than 3000 m3 per hour
per animal (average 1591 m3 per hour per animal). It is therefore very likely that air velocity
at floor level are also greater than in mechanically ventilated building. At the same time
inside temperatures are close to outside conditions.
3
3.2 Combined effect of temperature en air velocity for natural and mechanical
ventilation
To estimate the combined effect of temperature and air velocity in both naturally and
mechanically ventilated building combination of parameters was defined (Table 7).
Table 7
T-outside
5
10
15
20
Parameters for emission calculations
Natural
T-inside
7
12
17
22
T-pits
10
10
15
15
V-floor
0.1
0.2
0.3
0.4
V-pits
0.04
0.07
0.10
0.13
Mechanical
T-inside
9
14
19
24
V-floor
0.04
0.06
0.08
0.1
V-pits
0.01
0.02
0.03
0.04
T-inside is always 2 degrees higher than T-outside for naturally ventilated buildings and 4
degrees higher for mechanically ventilated building.
Air velocity in pits is coupled to air velocity at floor level. Relative differences are equal. The
temperature in pits is constant at 10oC when T-outside is 5 and 10 oC (winter) and 15 oC for
T-outside is 15 and 20 oC (summer). All combinations of T-inside and T-pits on one hand and
V-floor and V-pit on the other hand have been calculated for both mechanically and naturally
ventilated buildings.
Result are presented in figure 1 as a relative emission of the emission calculated with the
parameters given in table 2. That emission was 175.9 gram NH3/hour.
Figure 1
Relative emission under different circumstances. Legend: V-floor/V-pits
It can be concluded that air velocity contributes more to total emission than temperature and
that the ammonia emission from naturally ventilated buildings is higher than from buildings
with mechanical ventilation based on assumptions regarding ventilation rates and air velocity
at floor level.
An estimation of emission based on results from mechanically ventilated buildings would
probably underestimate the total (national) emission of ammonia, given the fact that 90% of
the animal buildings for dairy are naturally ventilated.
4
References
CIGR (2002) 4th Report of Working Group on Climatization of animal houses. Heat and
moisture production at animal and house levels. Eds.: S. Pedersen and K. Sällvik.
Duinkerken, G. van, G. André, M.C.J. Smits, G.J. Monteny, K. Blanken, M.J.M. Wagemans,
L.B.J. Šebek (2003), Relatie tussen voeding en ammoniakemissie uit de melkveestal, In
Dutch with summery in English, PraktijkRapport Rundvee 25, Praktijkonderzoek Veehouderij,
Lelystad, 66p.
Monteny, G.J., S.S. Schulte, A. Elzing, E.J.J. Lamaker (1998) A conceptual mechanistic
model for the ammonia emissions from free stall cubicle dairy cow houses. Transactions of
the ASAE, 41 (1) pp. 193-201.
Mosquera, J., J.M.G. Hol, C.M. Groenestein (2010) Evaluation of the CIGR method for
ventilation rate calculations from animal houses, Evaluatie van de CIGR methode voor de
bepaling van het ventilatiedebiet uit stallen, In Dutch with summary in english, Rapport 429,
Wageningen UR Livestock Research, Lelystad.
Mosquera, J., J.M.G. Hol, A. Winkel, J.W.H. Huis in ‘t Veld. F.A. Gerrits, N.W.M. Ogink,
A.J.A. Aarnink (2011 revised version), Dust emissioin from animal houses: dairy cattle,
Fijnstofemissie uit stallen: melkvee In Dutch with summary in English, Rapport 296,
Wageningen UR Livestock Research, Lelystad.
Ouwerkerk, E.N.J. van, 1999. ANIPRO klimaat- en energiesimulatiesoftware voor stallen.
IMAG Nota V 99-109, Wageningen, 87 pp.
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