Geijn, F., van de

Montsma, M.P.

Wageningen Yield 

Comparison of Univeg storage 
locations 
 
M. Montsma 
F. van de Geijn 
 
 
Report 1518   
Colophon 
 
Title Comparison of Univeg storage locations 
Author(s) M. Montsma 
F. van de Geijn 
Number 1518 
ISBN-number 978-94-6257-356-7 
Date of publication 15 December 2014 
Confidentiality No 
OPD code -- 
Approved by Ben Langelaan 
 
Wageningen UR Food & Biobased Research 
P.O. Box 17 
NL-6700 AA Wageningen 
Tel: +31 (0)317 480 084 
E-mail: info.fbr@wur.nl 
Internet: www.wur.nl 
 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig 
Onderzoek 
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system of any nature, or transmitted, in any form 
or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publisher. The publisher 
does not accept any liability for inaccuracies in this report. 
 
 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 2 
Abstract  
 
On request of Univeg Waddinxveen, Wageningen UR Food & Biobased Research has studied the 
technical specifications of three different storage locations. 
 
- Univeg Waddinxveen 
- RFW, Rotterdam Fruit Warf 
- NordFrost 
 
The technical information has been provided by Univeg in cooperation with each location. After 
comparing the data, the main differences between the facilities were pointed out. The main 
question was if the technical differences cause local “hot spots” or high humidity zones. 
Technical differences in settings and the effect on the quality of storage conditions and product 
quality was not part of this study.  
Besides the facility comparison some operational research of (product) temperature within the 
main storage rooms has been done for the Univeg Waddinxveen location. These measurements 
were carried out by staff members of Univeg . The results were interpreted and discussed by 
Wageningen UR. 
The results of these temperature studies give an indication of the specific (product) temperature 
range and show only differences that are accepted in storage practise. According to the 
experience of Wageningen UR Food & Biobased Research, the identified temperature profile is 
good. Depending on some operational variables, like product temperatures on arrival, the 
temperature difference within the room may be larger. The main advice is to set up a clear 
product temperature control and policy on adjustments of settings, based on the measurements 
of product temperature, settings of temperature control and air circulation.  
 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 3 
Content 
Abstract 3 
1 Introduction 5 
2 Results 6 
2.1 Technical comparison storage locations 6 
2.2 Temperature measurements Univeg Waddinxveen 8 
3 Conclusions 11 
 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 4 
1 Introduction 
 
Wageningen UR Food & Biobased Research has been asked to identify and explain possible 
impact of those differences in storage behaviour of different storage locations. The cold rooms 
who were part of this study were at the following locations: 
- Univeg Waddinxveen 
- RFW, Rotterdam Fruit Warf 
- NordFrost 
The facilities were compared, based on the available and relevant technical information provided 
by staff members and an expert visit of each location. At all locations cold rooms used for 
“longer” storage periods were studied. Longer storage is defined as longer than three weeks. In 
section 2 of this report the results of the technical comparison are described. The influence of 
operational handling and the effects of the technical difference on the product quality are no part 
of this study. 
 
Based on the technical comparison between the three locations the translation to actual storage 
conditions cannot be made. Therefore Wageningen UR Food & Biobased suggested to measure 
the air and product temperature during operation at the Univeg Waddinxveen location. The 
difference of temperature (product and air) at most critical positions in the storage room give the 
right information about temperature transfer between product and air, or in other words the air 
distribution. During several runs of 6-8 days the temperature has been monitored in two different 
cold rooms.   
 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 5 
2 Results 
The results of this study consist of two parts, first the technical comparison between the 
locations Waddinxveen, RFW and NordFrost and second the temperature measurements at the 
Univeg location in Waddinxveen. 
2.1 Technical comparison storage locations 
 
Dimensions and configuration 
In Table 1 the dimensions and configuration of the three compared storage rooms are described. 
In Figure 1 the differences in rack positions and the evaporator position with the air outlet 
direction are shown. 
 
Table 1: Dimensions and configuration of the three different cold rooms. 
 Univeg Nordfrost RFW 
Dimensions 25.6*16.2*10.8=4501m3 61.5*6*12.2=4513m3 600*10=6000m3 
# racks 2 2 2 
# pallets on rack (17*5*3)*2=510 (54*1*4)*2=432 (25.5*5*3)*2=765 
 
      
Figure 1: Schematic overview of the rack and evaporator position. The arrows indicate the direction of the cooling air 
outlet. 
 
Cooling, circulation and ventilation capacity 
Besides the different dimensions of the room, the position of the evaporator (cooler), the rack 
system (single, triple), the pallet position/stacking (in relation with the airflow direction) is 
different. The above mentioned items have impact on the air distribution and thus the 
temperature profile in the storage room.  
 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 6 
Table 2: Technical information related to cooling, circulation and ventilation capacity of three storage rooms. 
 Univeg Nordfrost RFW 
Cooling capacity 2*53=106kW 2*40=80kW 3*29.3=87.9kW 
Capacity per ton 0.26kW/ton 0.23kW/ton 0.14kW/ton 
Airflow coolers 2*42900=85800m3/h 2*42000=84000m3/h 3*33970=101910m3/h 
Air circulation 22.4 times 21.9 times 20.0 times 
Fresh air capacity 0.2 times/h 1.5 times/h 0.23 times/h 
Exchange surface 6.7m2/pallet /section 8.3m2/pallet /section 6.7m2/pallet /section 
 
The main technical parameters of cooling, circulation and ventilation are shown in Table 2. The 
cooling capacity of RFW is low compared to the other locations (in kW/ton). The capacity of the 
evaporator depends on the temperature difference between air temperature and the temperature 
of the (evaporating) coolant. This has been taken into account in this study.  
 
The fresh air capacity is 6-7 times larger at the Nordfrost location. For all locations the 
operational time of fresh air ventilation is not known. At the Nordfrost location the ventilation 
can be regulated by CO2 measurements. At the other locations no CO2 measurements are 
available. 
 
We expect that the air exchange surface of each pallet is important for a proper heat and moist 
exchange between pallet and air. Because of the rack system design the Nordfrost location has 
the largest exchange surface. 
 
Technical difference in measurements and control 
In Table 3 an overview is given of the measurements and control options of the measured 
parameters. 
 
Table 3: Measurement parameters and control options. 
 Univeg Nordfrost RFW 
# T-sensors 1 1 2 
# RH-sensors No 1 2 
Humidity control No Yes No 
CO2 -measurement No Yes No 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 7 
At all three locations temperature is measured and controlled by the cooling system. Humidity is 
monitored at Nordfrost and RFW. Univeg Waddinxveen doesn’t have humidity control. The 
humidity control of Nordfrost is based on cooling/heating air inlet (fresh air), heat exchanger air 
inlet – exhaust air and steam humidifier of the fresh air inlet. CO2 control is based on fresh air 
ventilation. Only at Nordfrost this is based on CO2 measurement, although the control setting 
may cause excessive ventilation and dehydration.  
2.2 Temperature measurements Univeg Waddinxveen 
 
The temperature (air and product) has been monitored with temperature loggers. The loggers 
were calibrated at a stable temperature. The positions of the loggers were defined by Wageningen 
UR and scheduled below (see Figure 2). The expected warmest and coldest positions were 
chosen. 
 
      
Figure 2: Schematic overview of side and top view of the storage room. The dots are sensor positions, where the dots in 
rectangular marked are also product temperature positions. The sides are marked with A and B. On the right the 
picture shows how sensors placed in the pallet. 
The focus of the temperature measurements is on the product temperature. The air temperature 
measurements at several positions are available. 
 
Run 1 
 
 
Figure 3: Room 6, run 1, product temperature measurement on side (rack) A and B, position p3, p4 and p5. 
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Ap3 Meetwaarden (ｰC) 
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Ap5 Meetwaarden (ｰC) 
Bp3 Meetwaarden (ｰC) 
Bp4 Meetwaarden (ｰC) 
Bp5 Meetwaarden (ｰC) 
B 
 
A 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 8 
 
The differences in product temperature (side A and B) at evaporator side and backside of the 
room are acceptable. Even the product temperature seems to decrease during the night time. 
Based on these measurements there seems to be a different temperature setting during the 
registration. The most variable temperatures in time will probably respond more directly to the 
average air temperature. 
 
Run 2 
In run 2 all six product sensors were placed in the rack of side A. Figure 4 shows the 
measurement results of the product temperature. 
 
Figure 4: Room 6, run 2, the six product sensors are all positioned at side A. 
The difference in product temperature between coldest and warmest position is relatively good. 
The temperature at position 4 is relatively warm, position 6 is cold. At these positions verification 
of correct temperature registration has been done. There is no clear explanation for the 
difference. To solve specific hotspots in cold rooms we have good experience with local forced 
circulation. An example of a mobile fan is shown in Figure 5. Such a circulation must be 
controlled with specific temperature measurements. Extra circulation without reason only uses 
energy and increases the heat load of the room. 
 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 9 
 
Figure 5: A mobile fan used for extra circulation. 
 
Run 3 
In run 3 the measurements are similar as in run 1 but carried out in room 2. 
 
 
Figure 6: Room 2, run 3, product temperatures at side (rack) A and B, position p3, p4 and p5. 
 
The variation of product temperatures in room 2 seems to be depending on specific stacking. 
Side A shows higher temperatures compared to side B. Within the rack the difference between 
position 3, 4 and 5 are small. The air temperature is not functional in finding the right product 
temperature. Only by measuring product temperature at several (critical) positions, the right 
settings can be chosen. With mobile fans the hot spot can be ventilated. 
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 10 
3 Conclusions 
 
Technical comparison 
Based on the available information of the technical comparison the indications are:  
 
Pallet configuration 
 Single rack systems > bigger exchange surface = better heat exchange with cooling air. 
 
Cooling capacity and circulation 
 For all locations the cooling capacity is similar. 
 Air circulation determines heat exchange (air – product). 
 Product temperature difference at different/extreme locations in the room is what really 
matters. 
 
Fresh air supply 
 Necessary for ethylene and CO2 removal. 
 For pears all locations have enough fresh air ventilation capacity. 
 Ethylene removal is less important for pears. 
 
CO2 control is important for pears 
 Frequent fresh air ventilation based on the measurements is sufficient. 
 Measurement range up to 0.2% CO2 can cause excessive ventilation (0.7% CO2 is 
allowed). 
 
Humidity control 
 Necessary to avoid dehydration (with humidifying) and to avoid fungal growth and rot 
(drying). 
 Humidity control of fresh air is an advantage because outside air normally has a high 
moisture load. 
 
Temperature measurements 
The temperature measurements of the product at different positions (see Figure 2) in room 2 and 
6 during several logging periods give an indication of the product temperature difference within 
the rooms (see Figure 3, Figure 4 and Figure 6). This difference is acceptable and similar with 
measurements at other storage locations.  
 
For optimal settings in temperature, circulation and control of optimal product temperatures 
monitoring of product temperatures is needed. These product temperature sensors can be hidden 
within the rack system (protected from the air) to simulate the buffer working of the product in 
the pallet.   
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 11 
General conclusion 
The general conclusion is that based on the technical layout, compared with the other two 
locations and especially based on the product temperature measurements, the storage potential of 
the Univeg Waddinxveen location is good. The measured temperature differences within the 
room are acceptable for the operation of pear storage.  
In order to optimize the storage conditions, especially important for storage times more than two 
months, more attention must be paid to product temperature differences within the room and 
improved air circulation.  
© Wageningen UR Food & Biobased Research, institute within the legal entity Stichting Dienst Landbouwkundig Onderzoek 12 


Comparison of Univeg storage locations

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