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Heat and Moisture Relevant In-Situ Measurements in a Railway Passenger Vehicle Driving Through the Swiss Alpine Region

January 2022
SSRN Electronic Journal

DOI:10.2139/ssrn.4082644

Authors:

Karim Ghazi Wakili

IABP and Bern University of Applied Sciences (BFH)

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Measured air temperature in the passenger compartment IT1 and beneath the window S3T2 and S3T4 (see Figure 5), as well as the heating power HP.

…

Measured relative humidity of the external air ERH1 and ERH2 (see Figure 7).

…

Maximum air speed for main line rolling stock according to EN 13129-1 [3].

…

Summary of the characteristics of the sensors/equipment used in this investigation. The sensors belonging to the University of Basel, who kindly shared the measured data, are shown in gray.

…

Measured relative humidity of the internal air during the measuring period (MM-monthly mean value).

…

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Citation: Raedle, W.; Wakili, K.G.;

Geyer, C.; Hausammann, R.;

Uehlinger, U. Heat and Moisture

Relevant In Situ Measurements in a

Railway Passenger Vehicle Driving

through the Swiss Alpine Region.

Sustainability 2022,14, 7462. https://

doi.org/10.3390/su14127462

Academic Editors: Pietro Evangelista,

Mladen Jardas, Predrag Brlek,

David Brˇci´c, Zlatko Sovreski and

Ljudevit Krpan

Received: 25 April 2022

Accepted: 16 June 2022

Published: 18 June 2022

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4.0/).

sustainability

Article

Heat and Moisture Relevant In Situ Measurements in a Railway

Passenger Vehicle Driving through the Swiss Alpine Region

Wolfgang Raedle, K. Ghazi Wakili *, Christoph Geyer, Roman Hausammann and Urs Uehlinger

Institute for Timber Construction, Structures and Architecture, Bern University of Applied Sciences (BFH),

Solothurnstrasse 102, 6, CH-2500 Biel, Switzerland; wolfgang.raedle@bfh.ch (W.R.);

christoph.geyer@bfh.ch (C.G.); roman.hausammann@bfh.ch (R.H.); urs.uehlinger@bfh.ch (U.U.)

*Correspondence: karim.ghaziwakili@bfh.ch; Tel.: +41-32-344-03-75

Abstract:

Transportation is a major sector of energy consumption in most, if not in all, European

countries. Besides the energy used for traction, energy is also consumed for ventilation, heating, and

cooling inside the vehicles to assure traveler comfort. This issue gains increasing importance as the

demand for public transport increases in the future. There is a need for retroﬁt to improve the thermal

resistance of the envelope of existing vehicles to reduce the heat loss to the environment during the

cold period of the year, especially in the Alpine region. A major concern in adding insulation material

to the envelope is the possibility of convective moisture transfer due to air circulation in the vehicle,

which would cause condensation accumulation on the cold surfaces. The present investigation

addresses this topic by measuring surface and air temperature, air moisture, air ﬂow, and heat ﬂow

at several critical locations of a vehicle during its travel in the Swiss Alpine region over several

months during the cold period of the year. Temperature measurements showed the potential of

reducing the heat losses in some parts of the vehicle. The level and duration of the moisture exposure

did not suggest a relevant formation of condensation in the cross-section of the vehicle wall. The

observed increase in relative humidity when driving through tunnels is too short to cause relevant

condensation in the vehicle shell. The measured low air ﬂow justiﬁes the assumption that no forced

convection occurs in the envelope cavities.

Keywords:

railway vehicle; in situ measurement; vehicle envelope; moisture transfer; retroﬁt;

heat loss

1. Introduction

In Switzerland, the primary sector in terms of energy consumption is transportation.

It accounted for more than one third, or 37.7%, of energy consumption for 2020, with an

increasing trend, according to the Swiss Federal Statistical Ofﬁce [

]. Increasing population

and encouragement of the government to use public transport will increase the demand in

the future. Besides the energy used for traction, the main energy is consumed by ventilation,

heating, and cooling required to provide a comfortable environment for travelers. It is

straightforward that the envelope and the windows of the passenger vehicles have a

decisive inﬂuence in this respect, as they are the barrier between the interior and exterior

climates. Secondary factors are the cooling, heating, and ventilation aggregates responsible

for keeping the interior climatic conditions in compliance with comfort requirements during

the summer and the winter period.

The thermal transmittance of a vehicle envelope can be determined for steady state

conditions, but in real use, it is dependent on many parameters, and it varies with them as

they change over time. Air circulation within the envelope structure and moisture uptake

of the insulation material, resulting in convective heat and mass transfer, are the most

inﬂuential of these parameters. In mountainous regions, it is during the heating period

(fall and winter) that the inﬂuence of these parameters becomes perceptible. Convective

moisture transfer into the porous insulation material can cause condensation and at low

Sustainability 2022,14, 7462. https://doi.org/10.3390/su14127462 https://www.mdpi.com/journal/sustainability

Sustainability 2022,14, 7462 2 of 20

temperatures, even enable the formation of ice, which reduces the insulating property.

Different insulation materials have different moisture uptake behaviors, which means that

the knowledge of the hygrothermal conditions in the envelope is vital in the selection of

the most appropriate insulation material for the vehicle envelope.

One of the earliest articles providing an overview of the current requirements for

air conditioning systems in rail vehicles was by Haller [

]. In a detailed analysis of the

comfort parameters based on the requirements of the respective standard EN 13129 [

it presented all the possible ways of improving thermal comfort. It was designed as a

guideline for railway operators, rail vehicle manufacturers, and manufacturers of air-

conditioning systems.

Following the above standard [

], the climatological operating conditions for summer

and winter are divided into three climatic zones, namely Southern Europe, Central Europe,

and Northern Europe, shown in Table 1. The corresponding maximum air speed in the

interior is also stated in the standard, depending on the local interior air temperature

(Table 2).

Table 1.

Design conditions for maximum mean interior temperature/relative humidity for main line

rolling stock according to EN 13129-1 [3].

Climatic Zones Tmax/rh max

Summer

All seats occupied

I+40 ◦C/40% rh; 800 W/m2+27 ◦C/51.6% rh

II +35 ◦C/50% rh; 700 W/m2+27 ◦C/51.6% rh

III +28 ◦C/45 % rh; 600 W/m225.3 ◦C/57.5% rh

Winter

With wind but without solar load

I−10 ◦C +22 ◦C

II −20 ◦C +22 ◦C

III −40 ◦C +22 ◦C

Table 2. Maximum air speed for main line rolling stock according to EN 13129-1 [3].

Local Interior Air Temperature TiMax. Air Speed in the Interior

+22 ◦C 0.25 m/s

+27 ◦C 0.60 m/s

A mathematic model to simulate the dynamic cooling load of an air-conditioned train

compartment was proposed by Liu et al. [

], showing that calculating the dynamic cooling

load can provide an adequate basis to determine the cooling load for trains traveling in dif-

ferent regions and seasons. Barone et al. [

] also proposed a dynamic simulation approach

for energy, economic, and environmental impact, along with thermal comfort analyses.

A study focused on the transparent portion of the envelope has been reported by

Bouvard et al. [

], where the impact of the solar gains on the HVAC energy consumption of

a panoramic train (large windows) has been investigated. They showed that the incoming

energy due to the solar gains is in the same order of magnitude as required for the heating

or cooling systems, and that an appropriate choice of the glazing can lead to energy savings

of 7 to 13%, depending on the climate.

Regarding heating and cooling in light rail vehicles, Beusen et al. [

] reported on a

detailed monitoring campaign resulting in an optimized strategy, reducing the respective

energy consumption under the climatic conditions of Flanders, Belgium. Chang et al. [

]

have analyzed the energy use and environmental emissions of high-speed rail transporta-

tion in China, without elaborating on the envelope materials and their thermal properties.

A study presented by Chow [

] dealing with the ventilation requirements in the train com-

partments of railway lines in Hong Kong found that to keep the carbon-dioxide level in the

train compartment low, a high ventilation rate must be provided. Gonzalez-Gil et al. [

]

reported that, without going more into detail, auxiliaries’ energy consumption of a single

Sustainability 2022,14, 7462 3 of 20

vehicle per passenger-km for a predeﬁned duty cycle is one of 12 key performance indica-

tors. A more elaborate investigation regarding the optimal control of thermal comfort in

trams has been performed by Hofstädter et al. [

]. Here too, simple assumptions were

made regarding the heat transfer through the envelope, without referring to effectively mea-

sured data. Lin et al. analyzed the thermal comfort of passengers in short- and long-haul

vehicles by involving simultaneous physical measurements and a questionnaire survey,

collecting data from 2129 respondents. They reported a neutral temperature of 27

◦

C and

a corresponding comfort zone for both types of vehicles between 22

◦

C and 29

◦

C [

A model to simulate the dynamic evolution of the temperature inside an air-conditioned

high-speed train compartment has been presented and investigated by Mastrullo et al.,

focusing mainly on refrigerant alternatives, but without any in situ measured data [

There are further surveys carried out regarding thermal comfort in rail cars [

], but without

any measurements of temperature or relative humidity in different parts of the envelope to

point out possible risks of condensation.

Powell et al. have shown in their comprehensive investigation that the energy con-

sumed by stabled vehicles is not negligible compared to the energy consumption of vehicles

in service, and found that about 11% of the yearly energy consumption is accounted for

by on-board auxiliary systems while the vehicle is stabled. Heating has been shown to be

responsible for about 45% of this consumption [

]. Finally, Wernery et al. evaluated the

use of superinsulation materials in trains to reduce heating/cooling demand [

]. They

screened and benchmarked selected commercially available superinsulation materials in

terms of thermal conductivity, ﬁre safety, behavior under vibration and preferred use

position within the train envelope. A previous study [

] on modeling the energy balance

of a Swiss railway wagon showed that 55% of the heat losses are experienced through the

envelope of the wagon (transmission losses) and 37% through the exhaust air of the ventila-

tion system. There was another study [

] which included the monitoring of six vehicles of

four different railway companies during several years, in which the climatic processes in

the cross-section of the vehicle envelope were also discussed, without investigating them in

detail. The assumption in the mentioned study [

] was that the following relevant factors

occur in the cross-section of the vehicle wall:

Formation of condensation between the outer shell and the thermal insulation of

rail vehicles;

- Ice formation between the outer shell and the thermal insulation of rail vehicles;

Strong air currents between the inner lining and the thermal insulation due to pressure

differences (between the passenger compartment and the outside climate) caused by

the ventilation system of the rail vehicles.

It was not examined or proven whether these factors actually occur in the cross-section

of a vehicle wall or not.

For answering these questions, the present study was based on heat and moisture

relevant in situ measurements in a railway passenger vehicle for a period of 7 months

during the cold season in the Swiss Alpine region. The measured data incorporated

temperature, relative humidity, heat ﬂow, and air ﬂow at different critical parts of the

vehicle and was recorded during the normal schedule of the train in this period of the year.

This included stops, ingress and egress of passengers, and passages through tunnels on

the way back and forth between the start and ﬁnal stations. Based on the analysis of the

measurements performed under real conditions, recommendations regarding the choice of

insulating material and their positioning in the vehicle envelope have been formulated to

reduce heat loss as a retroﬁt measure.

2. Measuring Equipment

Based on experience acquired during former research projects [

] dealing with

energy efﬁcient HVAC of railways passenger vehicles, a number of different sensor types

were chosen for the present investigations to measure the following physical quantities:

•The temperature of the outside air;

Sustainability 2022,14, 7462 4 of 20

•The relative humidity of the outside air;

•The temperature of the air in the passenger compartment;

•The relative humidity of the air in the passenger compartment;

•The surface temperature of the outer shell and the interior cladding;

•

The air temperature between the outer shell and the thermal insulation and between

the thermal insulation and the interior cladding;

•

The relative humidity between the outer shell and the thermal insulation and between

the thermal insulation and the interior cladding;

•The air speed between the interior cladding and the thermal insulation;

•The heat ﬂux density through the vehicle wall;

•

The pressure difference between the passenger compartment and the outside climate;

•The global radiation;

•

The energy meter, heating output, convective heating, and the passenger compartment.

2.1. Selection of Sensor Types

The selected sensors used for the present investigation are summarized in Table 3.

Table 3.

Summary of the characteristics of the sensors/equipment used in this investigation. The

sensors belonging to the University of Basel, who kindly shared the measured data, are shown in gray.

Sensor/Equipment Application Range Accuracy Supplier

Logger ALMEMO 5690-1 0.02% Ahlborn

Modem ZA 1 709 GPRS Ahlborn

Antenna GPS/GSM/UMTS/WLAN Ahlborn

Temp/RH sensor FHAD46C0L05 −40 ◦C to 85 ◦C

5 to 98% rh

±0.4 K

±4% Ahlborn

Thermocouple Type T −200 ◦C to 400 ◦C Ahlborn

Heat ﬂow sensor FQAD18T 0–26/0–260 mV ±5 % Ahlborn

Thermal anemometer FVAD35TH5K1 0.2 to 20 m/s +2% Ahlborn

Temp/RH sensor CMa20 indoor −20 ◦C to +55 ◦C

10% to 90% RH

±0.2◦K

±2% RH Elvaco

Temp/RH sensor CMa11 outdoor −40 ◦C to +55 ◦C

0 to 100% R

±0.5◦K

±2% RH Elvaco

Pressure difference

Solar Irradiation SP Lite 2 400 to 1100 nm 60 to 100 µV/W/m2Kipp & Zonen

GPS receiver EVK-6H u-blox

Energy meter DIZ-D651 3 ×230/400 VAC +15%, −20% ELKO

2.2. Positioning and Installation of Sensors

Several group of sensors have been built into the envelope at 3 different positions,

S1, S2, and S3 (Figure 1), and at 8 different sites of the vehicle (Figure 2). As the incoming

fresh air enters the vehicle after passing over a heating register and the exhaust air leaves

through the outer edges of the ceiling, there is no need to put sensors nearby those air

circulations. Further, the ﬂoor area was not accessible. Stadler Rail (the constructor of

the vehicle) has conﬁrmed that this can only be opened with great effort. In addition, the

radiators were located on the entire side of the car. For these reasons it was not necessary

to install sensors in this area.

Sustainability 2022,14, 7462 5 of 20

Sustainability 2022, 14, x FOR PEER REVIEW 5 of 21

radiators were located on the entire side of the car. For these reasons it was not necessary

to install sensors in this area.

Figure 1. RhB BDT 1751-58 vehicle. Vertical positions S1, S2, and S3 of sensor groups in the vehicle

envelope.

Figure 1.

RhB BDT 1751-58 vehicle. Vertical positions S1, S2, and S3 of sensor groups in the

vehicle envelope.

Sustainability 2022, 14, x FOR PEER REVIEW 5 of 21

radiators were located on the entire side of the car. For these reasons it was not necessary

to install sensors in this area.

Figure 1. RhB BDT 1751-58 vehicle. Vertical positions S1, S2, and S3 of sensor groups in the vehicle

envelope.

Figure 2.

RhB BDT 1751-58 vehicle. Horizontal positions S1, S2, and S3 of the sensor groups in the

vehicle envelope. These correspond to the positions in Figure 1.

Sustainability 2022,14, 7462 6 of 20

With the introduction of the NEVA Retica timetable concept in November 1999, the

Rhaetian Railway (RhB) put the BDt 1751-58 vehicle, built by Stadler Rail, into service. Var-

ious locomotives can be remotely controlled with these universal control cars. The vehicles

approved for 100 km/h have a low-ﬂoor area between the bogies and a driver’s brake

valve to control the vacuum train brake; the cars themselves are braked by compressed

air via a proportional valve. Since December 2004, three BDt vehicles have been running

between Landquart and Davos, and another three between Pontresina and Scuol-Tarasp.

2.3. Sensor Group S1

The structure of this area consists of the external cladding made of extruded aluminum

proﬁles, 40 mm thermal insulation, and an air cavity of 16 mm between the thermal

insulation and the interior cladding made of glass reinforced plastic (GRP). The sensors of

this group are shown in Figure 3.

Sustainability 2022, 14, x FOR PEER REVIEW 6 of 21

Figure 2. RhB BDT 1751-58 vehicle. Horizontal positions S1, S2, and S3 of the sensor groups in the

vehicle envelope. These correspond to the positions in Figure 1.

With the introduction of the NEVA Retica timetable concept in November 1999, the

Rhaetian Railway (RhB) put the BDt 1751-58 vehicle, built by Stadler Rail, into service.

Various locomotives can be remotely controlled with these universal control cars. The ve-

hicles approved for 100 km/h have a low-floor area between the bogies and a driver’s

brake valve to control the vacuum train brake; the cars themselves are braked by com-

pressed air via a proportional valve. Since December 2004, three BDt vehicles have been

running between Landquart and Davos, and another three between Pontresina and Scuol-

Tarasp.

2.3. Sensor Group S1

The structure of this area consists of the external cladding made of extruded alumi-

num profiles, 40 mm thermal insulation, and an air cavity of 16 mm between the thermal

insulation and the interior cladding made of glass reinforced plastic (GRP). The sensors

of this group are shown in Figure 3.

Figure 3. Type of sensors of Group S1 and their position in the vehicle.

2.4. Sensor Group S2

The structure of this area consists of the outer cladding made of extruded aluminum

with hollow chamber profiles, 20 mm thermal insulation, and an air cavity of 16 mm be-

tween the thermal insulation and the interior cladding made of glass reinforced plastic

(GRP). The insulation foam is compressible and can be slightly pressed by installing a heat

flow plate for good contact. The sensors of this group are shown in Figure 4.

Figure 3. Type of sensors of Group S1 and their position in the vehicle.

2.4. Sensor Group S2

The structure of this area consists of the outer cladding made of extruded aluminum

with hollow chamber proﬁles, 20 mm thermal insulation, and an air cavity of 16 mm

between the thermal insulation and the interior cladding made of glass reinforced plastic

(GRP). The insulation foam is compressible and can be slightly pressed by installing a heat

ﬂow plate for good contact. The sensors of this group are shown in Figure 4.

Sustainability 2022, 14, x FOR PEER REVIEW 7 of 21

Figure 4. Type of sensors of Group S2 and their position in the vehicle.

2.5. Sensor Group S3

The structure of this area also consists of an aluminum exterior cladding (40 mm of

thermal insulation with a vapor barrier and an air cavity of 16–19 mm) between the ther-

mal insulation and the interior cladding. The insulation is compressible and can be

pressed by installing a heat flow plate for good contact. The sensors of this group are

shown in Figure 5.

Figure 5. Type of sensors of Group S3 and their position in the vehicle.

2.6. Sensors for the Internal Air

There were four additional combined temperature and relative humidity sensors in-

stalled to measure the internal air in the compartments (IT1, IRH1/IT2, IRH2/IT3,

IRH3/IT4, IRH4). They were positioned so that the measured values represent an average

room climate during the monitoring period.

2.7. Sensor Installation

The thermocouples were fixed directly onto the outer shell with an aluminum adhe-

sive tape towards the inner room. A combined temperature and moisture sensor was

glued between the outer shell and the thermal insulation. It is important that the insula-

tion is cut cleanly and fixed again after gluing the sensors, without any gaps or overlaps.

All other sensors were mounted using a frame with a bar (Figure 6). The whole unit

was screwed or glued to the interior cladding. The bars in the frame are dimensioned in

Figure 4. Type of sensors of Group S2 and their position in the vehicle.

Sustainability 2022,14, 7462 7 of 20

2.5. Sensor Group S3

The structure of this area also consists of an aluminum exterior cladding (40 mm of

thermal insulation with a vapor barrier and an air cavity of 16–19 mm) between the thermal

insulation and the interior cladding. The insulation is compressible and can be pressed

by installing a heat ﬂow plate for good contact. The sensors of this group are shown in

Figure 5.

Sustainability 2022, 14, x FOR PEER REVIEW 7 of 21

Figure 4. Type of sensors of Group S2 and their position in the vehicle.

2.5. Sensor Group S3

The structure of this area also consists of an aluminum exterior cladding (40 mm of

thermal insulation with a vapor barrier and an air cavity of 16–19 mm) between the ther-

mal insulation and the interior cladding. The insulation is compressible and can be

pressed by installing a heat flow plate for good contact. The sensors of this group are

shown in Figure 5.

Figure 5. Type of sensors of Group S3 and their position in the vehicle.

2.6. Sensors for the Internal Air

There were four additional combined temperature and relative humidity sensors in-

stalled to measure the internal air in the compartments (IT1, IRH1/IT2, IRH2/IT3,

IRH3/IT4, IRH4). They were positioned so that the measured values represent an average

room climate during the monitoring period.

2.7. Sensor Installation

The thermocouples were fixed directly onto the outer shell with an aluminum adhe-

sive tape towards the inner room. A combined temperature and moisture sensor was

glued between the outer shell and the thermal insulation. It is important that the insula-

tion is cut cleanly and fixed again after gluing the sensors, without any gaps or overlaps.

All other sensors were mounted using a frame with a bar (Figure 6). The whole unit

was screwed or glued to the interior cladding. The bars in the frame are dimensioned in

Figure 5. Type of sensors of Group S3 and their position in the vehicle.

2.6. Sensors for the Internal Air

There were four additional combined temperature and relative humidity sensors

installed to measure the internal air in the compartments (

IT1, IRH1/IT2, IRH2/IT3,

IRH3/IT4, IRH4

). They were positioned so that the measured values represent an av-

erage room climate during the monitoring period.

2.7. Sensor Installation

The thermocouples were ﬁxed directly onto the outer shell with an aluminum adhesive

tape towards the inner room. A combined temperature and moisture sensor was glued

between the outer shell and the thermal insulation. It is important that the insulation is cut

cleanly and ﬁxed again after gluing the sensors, without any gaps or overlaps.

All other sensors were mounted using a frame with a bar (Figure 6). The whole unit

was screwed or glued to the interior cladding. The bars in the frame are dimensioned in

such a way that the heat ﬂow plate is pressed lightly against the thermal insulation. This

ensures a correct measurement of the heat ﬂow without additional air gaps falsifying the

results. The exact distance was determined by measuring the free space after the interior

cladding had been dismantled.

Sustainability 2022,14, 7462 8 of 20

Sustainability 2022, 14, x FOR PEER REVIEW 8 of 21

such a way that the heat flow plate is pressed lightly against the thermal insulation. This

ensures a correct measurement of the heat flow without additional air gaps falsifying the

results. The exact distance was determined by measuring the free space after the interior

cladding had been dismantled.

Figure 6. Auxiliary construction for fastening the thermal anemometer (shiny metallic probe at the

bottom), the heat flow plate (gray square), and the combined air temperature and relative humidity

sensors (black) into their relative positions indicated in the previous figures.

This auxiliary construction has the following advantages:

The frame material is made of pine/epoxy resin (for better strength);

Recesses on the epoxy resin profile reduce the contact between the frame and the heat

flow meter plate (Figure 6);

The measurement is not influenced by highly thermally conductive materials;

The heat flow through the aluminum cladding of the thermal insulation is reduced by the

frame zone;

The complete unit can be attached or glued to the interior cladding with two screws;

The heat flow meter plate is pressed against the thermal insulation without gluing. The

exact distance was adjusted to the specific proportions/dimensions by adjusting the bars

before assembly;

Rounded frame edges reduce damage to the thermal insulation and the aluminum clad-

ding.

2.8. Data Acquisition

The acquisition rate of the system is 0.1 s, so it needs less than 5 s for reading 48

sensors. The measured values are saved once per minute. The memory is deleted after

successful data transfer.

2.9. GPRS Antenna, Pyranometer, and Sensors for External Air

With the exception of the GPRS Antenna, all other sensors belong to the University

of Basel, who kindly shared the measured data for the evaluations in this investigation.

The mentioned sensors position on the outer back-face of the vehicle is shown in Fig-

ure 7.

Figure 6.

Auxiliary construction for fastening the thermal anemometer (shiny metallic probe at the

bottom), the heat ﬂow plate (gray square), and the combined air temperature and relative humidity

sensors (black) into their relative positions indicated in the previous ﬁgures.

This auxiliary construction has the following advantages:

The frame material is made of pine/epoxy resin (for better strength);

Recesses on the epoxy resin proﬁle reduce the contact between the frame and the heat ﬂow

meter plate (Figure 6);

The measurement is not inﬂuenced by highly thermally conductive materials;

The heat ﬂow through the aluminum cladding of the thermal insulation is reduced by the

frame zone;

The complete unit can be attached or glued to the interior cladding with two screws;

The heat ﬂow meter plate is pressed against the thermal insulation without gluing. The

exact distance was adjusted to the speciﬁc proportions/dimensions by adjusting the bars

before assembly;

Rounded frame edges reduce damage to the thermal insulation and the aluminum cladding.

2.8. Data Acquisition

The acquisition rate of the system is 0.1 s, so it needs less than 5 s for reading 48

sensors. The measured values are saved once per minute. The memory is deleted after

successful data transfer.

2.9. GPRS Antenna, Pyranometer, and Sensors for External Air

With the exception of the GPRS Antenna, all other sensors belong to the University of

Basel, who kindly shared the measured data for the evaluations in this investigation.

The mentioned sensors position on the outer back-face of the vehicle is shown in

Figure 7.

Sustainability 2022,14, 7462 9 of 20

Sustainability 2022, 14, x FOR PEER REVIEW 9 of 21

Figure 7. Position of sensors for temperature and relative humidity of the external air, the GPRS

antenna and the two pyranometers on the outer back-face of the vehicle.

2.10. Power Supply

The power supply for the measuring equipment is ensured by the battery of the ve-

hicle. The measuring system restarts automatically after a power failure. The system is

therefore ready for operation again as soon as the vehicle is back in use.

2.11. The Path of the Vehicle

The route network of the Rhaetian Railway (the largest Alpine railway in Switzer-

land) is shown below in Figure 8. The route taken by the vehicle used for the present

investigation is shown in red color. The route contains a long passage through the Vereina

Tunnel, which shows an important impact on the measured data, as will be discussed

later.

Figure 8. The path of the vehicle during the in situ measurements (in red).

3. Results and Discussion

In the following sections, a representative part of all data measured in the period

beginning on 30 September 2017 and ending on 30 April 2018 (with a short gap of 20 days)

are presented and analyzed. This time interval represents a typical winter period in the

Swiss Alpine region. It is only during this period that climate-dependent and energy-rel-

evant measurements can be collected, as the indoor and outdoor temperatures differ the

most.

Figure 7.

Position of sensors for temperature and relative humidity of the external air, the GPRS

antenna and the two pyranometers on the outer back-face of the vehicle.

2.10. Power Supply

The power supply for the measuring equipment is ensured by the battery of the

vehicle. The measuring system restarts automatically after a power failure. The system is

therefore ready for operation again as soon as the vehicle is back in use.

2.11. The Path of the Vehicle

The route network of the Rhaetian Railway (the largest Alpine railway in Switzerland)

is shown below in Figure 8. The route taken by the vehicle used for the present investigation

is shown in red color. The route contains a long passage through the Vereina Tunnel, which

shows an important impact on the measured data, as will be discussed later.

Sustainability 2022, 14, x FOR PEER REVIEW 9 of 21

Figure 7. Position of sensors for temperature and relative humidity of the external air, the GPRS

antenna and the two pyranometers on the outer back-face of the vehicle.

2.10. Power Supply

The power supply for the measuring equipment is ensured by the battery of the ve-

hicle. The measuring system restarts automatically after a power failure. The system is

therefore ready for operation again as soon as the vehicle is back in use.

2.11. The Path of the Vehicle

The route network of the Rhaetian Railway (the largest Alpine railway in Switzer-

land) is shown below in Figure 8. The route taken by the vehicle used for the present

investigation is shown in red color. The route contains a long passage through the Vereina

Tunnel, which shows an important impact on the measured data, as will be discussed

later.

Figure 8. The path of the vehicle during the in situ measurements (in red).

3. Results and Discussion

In the following sections, a representative part of all data measured in the period

beginning on 30 September 2017 and ending on 30 April 2018 (with a short gap of 20 days)

are presented and analyzed. This time interval represents a typical winter period in the

Swiss Alpine region. It is only during this period that climate-dependent and energy-rel-

evant measurements can be collected, as the indoor and outdoor temperatures differ the

most.

Figure 8. The path of the vehicle during the in situ measurements (in red).

3. Results and Discussion

In the following sections, a representative part of all data measured in the period

beginning on 30 September 2017 and ending on 30 April 2018 (with a short gap of 20 days)

are presented and analyzed. This time interval represents a typical winter period in the

Swiss Alpine region. It is only during this period that climate-dependent and energy-

relevant measurements can be collected, as the indoor and outdoor temperatures differ

the most.

3.1. Temperature Measurements

A gap in the measured values was detected for the period from 18 December 2017 to 8

January 2018. Measured values were recorded during this time, but the transmission of the

Sustainability 2022,14, 7462 10 of 20

data from the vehicle to our data server failed during this period, and the corresponding

data was lost. Since we still have enough meaningful data for the evaluation period

(October 2017 up to and including April 2018), the loss of data in the mentioned period

does not pose a problem.

Figure 9shows the measured external air temperature

ET1

for the period between

24 September 2017

, and 6 May 2018, which represents the cold period of the year in the

Swiss Alpine region.

Sustainability 2022, 14, x FOR PEER REVIEW 10 of 21

3.1. Temperature Measurements

A gap in the measured values was detected for the period from 18 December 2017 to

8 January 2018. Measured values were recorded during this time, but the transmission of

the data from the vehicle to our data server failed during this period, and the correspond-

ing data was lost. Since we still have enough meaningful data for the evaluation period

(October 2017 up to and including April 2018), the loss of data in the mentioned period

does not pose a problem.

Figure 9 shows the measured external air temperature ET1 for the period between 24

September 2017, and 6 May 2018, which represents the cold period of the year in the Swiss

Alpine region.

Figure 9. Measured external air temperature ET1 from 24 Sep 2017 to 06 May 2018.

In periods of generally low outside temperatures, we repeatedly measure short peri-

ods of outside temperatures above 10 °C. Figure 10 shows this effect as an example for 28

February 2018. A spot check showed that this effect can be assigned to the tunnel passages

through the Vereina Tunnel and the Albula Tunnel.

09:52 a.m.: passage through the Vereina Tunnel in the direction of the Rhine Valley

12:25 p.m.: passage through the Vereina Tunnel in the direction of the Engadin

03:52 p.m.: passage through the Vereina Tunnel in the direction of the Rhine Valley

06:18 p.m.: passage through the Vereina Tunnel in the direction of the Engadin

08:30 p.m.: passage through the Vereina Tunnel in the direction of Tiefencastel

10:40 p.m.: passage through the Vereina Tunnel in the direction of the Engadin

ET1

Temperature [°C]

Date, time

Figure 9. Measured external air temperature ET1 from 24 September 2017 to 6 May 2018.

In periods of generally low outside temperatures, we repeatedly measure short pe-

riods of outside temperatures above 10

◦

C. Figure 10 shows this effect as an example

for

28 February 2018.

A spot check showed that this effect can be assigned to the tunnel

passages through the Vereina Tunnel and the Albula Tunnel.

Sustainability 2022, 14, x FOR PEER REVIEW 11 of 21

Figure 10. Measured external air temperature (ET1 and ET2, left y-axis) and GPS altitude (black,

right y-axis) for the whole day of 28 February 2018.

There is a slight difference between the two sensors ET1 and ET2 (dotted and full

blue lines in Figure 10). This might be due to several factors, such as different local expo-

sure to wind flow, solar irradiation, ice formation, or sensor accuracy. As they are consid-

ered as negligible, their discrepancy will not be followed further.

Figure 11 shows that during the evaluation period, the air temperature IT4 in the

passenger compartment is slightly higher than the air temperature in the luggage com-

partment IT2, and fluctuates less. This can be explained by the fact that the luggage com-

partment has no partition to the vehicle door; thus, the outside air can flow unhindered

into the luggage compartment when the door is opened. Further, Figure 11 shows the

nighttime reduction in heating in both the passenger compartment and the luggage com-

partment. One can also see that the night reduction does not occur every night. This is due

to shortcomings of the installation of relatively old control technology.

Figure 11. Measured air temperatures in the passenger room (IT4) and the luggage compartment

(IT2) from 17 February to 6 March 2018.

Figure 10.

Measured external air temperature (

ET1 and ET2

, left y-axis) and GPS altitude (black,

right y-axis) for the whole day of 28 February 2018.

Sustainability 2022,14, 7462 11 of 20

09:52 a.m.: passage through the Vereina Tunnel in the direction of the Rhine Valley

12:25 p.m.: passage through the Vereina Tunnel in the direction of the Engadin

03:52 p.m.: passage through the Vereina Tunnel in the direction of the Rhine Valley

06:18 p.m.: passage through the Vereina Tunnel in the direction of the Engadin

08:30 p.m.: passage through the Vereina Tunnel in the direction of Tiefencastel

10:40 p.m.: passage through the Vereina Tunnel in the direction of the Engadin

There is a slight difference between the two sensors

ET1

and

ET2

(dotted and full blue

lines in Figure 10). This might be due to several factors, such as different local exposure to

wind ﬂow, solar irradiation, ice formation, or sensor accuracy. As they are considered as

negligible, their discrepancy will not be followed further.

Figure 11 shows that during the evaluation period, the air temperature

IT4

in the pas-

senger compartment is slightly higher than the air temperature in the luggage compartment

IT2,

and ﬂuctuates less. This can be explained by the fact that the luggage compartment has

no partition to the vehicle door; thus, the outside air can ﬂow unhindered into the luggage

compartment when the door is opened. Further, Figure 11 shows the nighttime reduction

in heating in both the passenger compartment and the luggage compartment. One can also

see that the night reduction does not occur every night. This is due to shortcomings of the

installation of relatively old control technology.