Docstoc

Improvement of the Energy Efficiency of a Distribution Warehouse

Document Sample
Improvement of the Energy Efficiency of a Distribution Warehouse Powered By Docstoc
					Improvement of the Energy Efficiency of a Distribution Warehouse
in Madrid (Spain) with Special Emphasis on Daylight Optimisation
Cécile Bonnet, Joan Carles Bruno, Alberto Coronas
Universitat Rovira i Virgili - CREVER, Group of Applied Thermal Engineering


Abstract
This paper presents a technical study which has been realised by CREVER – Group of Applied
Thermal Engineering on an industrial building to be built in the province of Madrid with a total area of
33,795 m2. The main part of the building is used as warehouse and is thus neither heated nor cooled,
so that the energy demand is basically due to lighting. The building also includes two air-conditioned
office areas of 985 m2 each one.

As reference, another existing building with the same constructive characteristics, use and location
has been considered in order to evaluate the potential energy savings. In this building, it has been
evaluated that almost 84 % of the electricity demand is due to the warehouse lighting, 9 % to offices
(heating cooling, domestic hot water, lighting and other electrical equipments) and 7 % to battery load
of handling machines.

First, the efficiency of the planned lighting installation has been assessed, according to the references
of the Spanish Building Technical Code. Then, with the help of the daylight simulation software
DAYSIM, the saving potential through the use of a photocell controlled dimming system has been
evaluated. Also the increase of the daylight penetration through the use of roof glazing with higher
transmittance has been contemplated. The effect of the increased roof glazing transmittance on the
summer comfort conditions has been analysed with the help of the building energy simulation
software EnergyPlus (DesignBuilder interface).

The study concludes that energy savings of up to 25 % could be reached through the optimisation of
the warehouse lighting system implementing a photocell controlled dimming system and increasing
the sky glazing transmittance up to 30 %. The effect of the increased glazing transmittance on the
summer comfort conditions is considered to be reasonable. Additionally, the installation of PV panels
on the roof of the building is planned, which should permit to reduce the non-renewable energy
consumption of the building by additionally 25 %, reaching a global primary energy saving of almost
50 %.


1. Introduction and objectives of the study
The GreenBuilding Programme is a programme of European Commission which aims at encouraging
the implementation of energy efficiency measures in non-residential buildings. Both existing and new
non-residential buildings can take part to the programme. The condition for owners of new buildings to
become partners of GreenBuilding is to reduce the primary energy consumption of the building by at
least 25 % with respect to a reference building of similar characteristics. [1]

The objective of this study is to evaluate different alternatives to reduce the energy consumption of a
new industrial building for logistic use with respect to an existing building presenting the same
characteristics, use and location, in order to become a partner of the Programme. A special focus of
this study will be the reduction of the lighting electrical demand. This study has to be considered as a
preliminary study evaluating possible measures from an energy saving point of view. No economical
considerations are contemplated.

This paper is structured as follows. In section 2, it is presented the studied and reference building
used to evaluate the potential savings and also it is determined the corresponding energy demand of
the reference building. In section 3, it is presented the method used to evaluate the lighting efficiency
and the impacted associated with different improvement measures proposed. Finally, in section 4, are
summarised the benefits of the proposed energy improvement measures.
2. Presentation of the studied and the reference buildings
2.1. Presentation of the studied building

The object of this study is an industrial building to be built during 2008 in a logistic park located in the
province of Madrid.

The building, to be used as distribution warehouse includes a storage area of 31,824 m2 mainly
occupied by storage racks, as well as two 3-floor office sections of 985 m2 each one located on the
north-west and south-east facades (see Fig. 1), including offices and changing rooms.

Due to the use made of the building, the occupancy of the warehouse section is foreseen to be very
low and variable. Also in the office section, it is predicted a relatively low occupancy of about
20 pers / building corresponding to about 0.02 pers / m2.

The warehouse section will neither be heated nor cooled, for which the energy demand of this section
representing almost 94 % of the total building area, is exclusively related to lighting and battery load
of the handling machines. However, the office sections are air-conditioned with reversible air handling
units and additionally present usual energy demand for domestic hot water (DHW), lighting and other
electrical equipments.

         Figure 1: General view of the studied building showing one of the office areas




2.2. Presentation of the reference building

To enable comparisons and thus facilitate the assessment of the considered energy saving measures
in the considered building, a building with almost identical constructive characteristics, use and
location (both building being from the same real estate developer) is considered as reference building
in this study.

This building is in operation since October 2006. Real electricity consumption data for this reference
building is available from the electricity bills of the seven first month of operation of the building.

The buildings, besides being both located in the province of Madrid, present similar configurations
(location of office sections on the opposite façades), floor areas as well as roof inclinations and roof
glazing proportions.

                           Figure 2: General plan of the reference building
2.3. Repartition of the energy consumption by use (reference building)

2.3.1. Estimation of the annual energy consumption of the reference building

Both reference and studied buildings exclusively present electrical energy consumption. The
warehouse section has no thermal demand. In the office area, the thermal demand (heating and
cooling) is covered by an electric driven air handling units.

According to the seven first electricity bills of the reference building, an annual energy consumption of
1,323 MWh/a has been estimated, corresponding to 38 kWh/m2a.

This electricity consumption is due to warehouse lighting, battery load of handling machines, and
office requirements for heating, cooling, DHW, lighting and office equipment.


2.3.2. Estimation of the electricity consumption due to warehouse lighting

In order to evaluate which part of the electricity consumption is due to the warehouse lighting, a
daylight simulation of the warehouse has be realised using the daylight simulation tool DAYSIM [2].

The corresponding electricity demand for artificial lighting is largely dependent on the user behaviour.
Therefore, two user profiles have been considered in the simulation:

    -   an intermediate user profile with 50 % active users and 50 % passive users.
            o Active users operate the electrical lighting according to the ambient daylight
                conditions
            o Passive users do not operate the electrical lighting according to the ambient daylight
                conditions and keep the electrical lighting on throughout the working day.
    -   a passive user profile with 100 % passive users. [3]

A building occupation from 7 AM to 11 PM has been considered. An illuminance of 200 lux is required
in the warehouse. According the plans of the lighting installation of the reference building, a lighting
power of 8 W/m2 is installed in the warehouse.
As there are no windows on the building façade, the daylight only enters the building through
translucent roof glazing (polyester) which represents 17 % of the total roof area. The roof tilt is around
7 %.

The results of the simulation for the warehouse lighting are presented in table 1.

        Table 1: Estimation of the annual electricity consumption for warehouse lighting
             User profile                                        Intermediate     Passive
                                                         2
             Estimated annual electricity           kWh/m .a         33.4             36
             consumption
                                                    MWh/a           1,100            1,186


2.3.3. Estimation of the electricity demand of the office sections (reference building)

To evaluate the annual energy demand of the office buildings for heating, cooling, DHW, lighting and
office equipments, a thermal simulation has been performed using the simulation software EnergyPlus
[4] with the DesignBuilder interface [5].

The results of the DesignBuilder simulations are presented in table 2.

          Table 2: Annual final energy demand of the office areas (reference building)
                            North section                   South section            Total office sections
                                                2                             2
                        kWh/a          kWh/m a          kWh/a       kWh/m a          kWh/a       kWh/m2a
 TOTAL                  59,753           65.1           58,818         64.1          118,570        64.6



2.3.4. Estimation of the electricity consumption for battery charging of the handling machines

For battery charging, an annual electricity consumption of 93600 kWh has been estimated
considering a power of 60 W for 6 hours charging per day, 5 days a week and 52 weeks per year.


2.3.5. Conclusions - repartition of the energy demand by use

           Table 3: Distribution of the energy consumption by use (reference building)
                       Estimated energy demand according to simulations               Real
                                        Lighting user profile                    consumption
                           Intermediate                        Passive            (elect. bills)
                          kWh/a       % of total            kWh/a     % of total            kWh
                                      demand                           demand
 Warehouse
                      1,100,602         83.8            1,186,278       84.8
 lighting
 Offices                118,570          9.0              118,570        8.5
 Battery load             93,600         7.1               93,600        6.7
 Total                1,312,772                         1,398,448                     1,323,713
 Total /m2                  37.7 kWh/m2a                      40.2 kWh/m2a                 38.05

From these results, it can be concluded that the intermediate lighting user profile is the most coherent
with the real consumption data according to electricity bills. For instance, an intermediate user profile
will be considered as parameter in the following simulations to evaluate the energy saving potential
through daylight optimisation.

The results also confirm the hypothesis that the warehouse lighting represent the major part of the
electricity demand of the building and thus that the study has to concentrate on the reduction of this
demand.
3. Results
3.1. Assessment of the energy efficiency of the planned lighting installation

First of all, it is necessary to assess the energy efficiency of the planed lighting installation of the
considered building. For this purpose, the energy efficiency index of the warehouse and of each zone
of the office areas will be determined.

According to the new Spanish Building Technical Code (Código Técnico de la Edificación) part HE 3
[6], the energy efficiency Index IEE is defined as the lighting power installed per m2 lighted surface
and per 100 lux illuminance maintained in this zone.

                                   P ⋅ 100
                           IEE =                            in W /m2·100 lux
                                   S ⋅ Em
where

    -   P: installed lighting power [W]
    -   S: lighted surface [m2]
    -   Em: medium horizontal illuminance maintained [lux]

The Spanish Building Technical Code establishes maximum values for this index according the use
made of the considered area. These values will be used as reference to evaluate the efficiency of the
installation.

From the results (Table 4), it can be concluded that the energy efficiency index of the planned lighting
installation in the warehouse lies well below the critical value established by the Spanish Building
Technical Code for warehouse. Indeed, the selected lamps (fluorescent tubes and high pressure
sodium lamps) present a high luminous efficiency [7]



   Table 4: Evaluation of the efficiency of the planned lighting installation in the warehouse

                                                    Type of lamps

                                                                 High
                                             Fluorescent      pressure
                                                                               Total
                                                tubes          sodium
                                                                lamps
 Unit power                W                     58              400
 Number of lamps                                464              544
 Installed power           W                   26,912          217,600         244,512     W
 Corresponding area        m2                                                   32,952     m2
 Required illuminance      lux                                                     200     lux
 Calculated energy
                           W/m2100 lux                                            3.71     W/m2100 lux
 efficiency index
 Max. energy efficiency
                           W/m2100 lux                                                 5   W/m2100 lux
 index according to CTE




3.2. Evaluation of energy saving measures for warehouse lighting
The previous results showed that the energy efficiency of the planned installation is good and no
significant energy saving potentials can be associated to the change of the type of lamps. Therefore
the study has been focused on saving potentials in the lighting use.

A major way to reduce the lighting energy demand is to optimise the use of daylight by increasing the
daylight penetration and particularly by adapting the artificial light to the daylight availability through
the use of daylight sensors and dimmers.

In section 2.3.5, it has been determined that a large part of the users probably do not operate the
electrical lighting according to daylight conditions and often keep the light on throughout the working
day. However, considering the important area which is considered in this study (over 30,000 m2), the
low density of occupation, and the activities realised in the building (load and unload of goods
between storage racks and trucks implying almost constant movement), the use of occupancy
sensors in the warehouse section has not been contemplated as an adequate alternative.

On the other hand, the following alternatives will be simulated using the daylight simulation tool
DAYSIM [2] and compared with the reference building:

    -    Control of the artificial lighting system using daylight sensors (photocells) and dimmers
    -    Increase of the relative roof glazing area (with and without daylight control)
    -    Use of roof glazing with higher daylight transmittance (with and without daylight control)

These alternatives or measures are presented in detail in table 6.

  Table 6: Considered alternatives to reduce the energy consumption for warehouse lighting
Case           Roof glazing     Roof glazing        Daylight
                                                                  Description
studied        percentage       transmittance       control
Ref. Case      17               20                  no            Reference building
                                                                  Ref. case + photocell controlled
Case1pc        17               20                  yes
                                                                  dimmer
Case 2         21.3             20                  no            Increased roof glazing surface 21.3 %
Case2pc        21.3             20                  yes           Case 2 + photocell controlled dimmer
                                                                  Use of glazing material with higher
Case 3         17               30                  no
                                                                  transmittance (30 %)
Case 3pc       17               30                  yes           Case 3 + photocell controlled dimmer

In order to evaluate these measures, the daylight availability will be estimated using the following
factors:

    -    Daylight factor: it is defined as the ratio of the indoor illuminance at a point of interest to the
         outdoor horizontal illuminance under the overcast CIE sky. [3]
    -    Daylight autonomy: it is defined at a point in a building as the percentage of occupied hours
         per year, when the minimum illuminance level (lux) can be maintained by daylight alone. In
         contrast to the more commonly used daylight factor, the daylight autonomy considers all sky
         conditions throughout the year. [3]

The simulation will be realised for an intermediate user profile as it has been determined in
section 2.3.5.

The simulation includes an optimized regulable lighting control system with photocells. The regulation
of the artificial lighting with photocells permits to adequate the light intensity of the lamps according to
the quantity of daylight available.

Once the lamps have been manually activated through an on/off switch, the dimming system
regulates the artificial light so that the total illuminance (natural and artificial) reaches the minimum
required illuminance (here 200 lux). In case that the minimum required illuminance level is reached
only with daylight, the artificial light is automatically switched off [2]. The photocell stand-by power is
2 W. A ballast loss factor of 20 % has been considered.
The results are shown in Table 7. It can be concluded that the implementation of a daylight control
with photocells and dimmers should contribute to significant energy savings for the lighting of the
warehouse. With this measure and without any modification of the building envelope characteristics,
such a system should allow a reduction of the warehouse lighting energy consumption by 22.5 %.


             Table 7: Evaluation of the energy saving potential for warehouse lighting
                                Ref.
Case studied                                 Case 1pc    Case 2      Case 2.pc      Case 3      Case 3pc
                                Case
Roof glazing
                  %               17.0         17.0        21.3         21.3         17.0         17.0
percentage
Roof glazing
                  %               20            20          20           20           30            30
transmittance
Daylight
                               Manual       Photocells   Manual      Photocells     Manual     Photocells
control
Daylight factor   %              2.06          2.06        3.15         3.15         3.14         3.14
Daylight
                  %               57            57         63.4         63.4         62.7         62.7
autonomy
Estimated         kWh/m2.a        33.4         25.9        31.9         23.4         32.5         24.3
lighting energy
demand            MWh/a         1,101          853        1,051          771         1,071          801
                  MWh/a            0           247          49           330          30            300
Savings with
                         2
respect to ref.   kWh/m .a                     7.50        1.50         10.00        0.90         9.10
case
                  %                0           22.5        4.5          29.9          2.7         27.2


If this measure is combined with a higher daylight penetration through the use a roof glazing material
with higher daylight transmittance or the increase of the roof glazing surface, savings of up to 27 %
and 30 % respectively, could theoretically be reached.

However, an increase of the daylight penetration without daylight control system only produces limited
savings of only 4.5 % in case 2 and 2.7 % in case 3. This is due to a non-optimal user profile where
50 % of the users are considered to operate the artificial light in a passive way.


3.3. Influence of an increased daylight penetration on summer comfort conditions

The increase of the roof glazing area or the use of a material with higher daylight transmittance leads
to higher daylight penetration in the building and should thus permit to reduce the electric lighting
requirements. However this also means higher solar heat gains in summer which can lead to a
sensible increase of the operative temperature inside the warehouse, which is not air-conditioned.

Hence a thermal analysis of the warehouse using the EnergyPlus software [4] with DesignBuilder
interface [5] will be performed in order to analyse the summer comfort conditions for the case studied
(Ref. Case, case 2 and 3) in the previous section and for two additional cases with higher increase of
the daylight penetration through higher percentage of roof glazing (case 4 and 5).

This will be achieved by determining the number of hours per year by which the operative temperature
of the building is higher than 28 ºC.




            Table 8: Effect of the different measures on the summer comfort conditions
     Case         Percentage of          Transmittance      Percentage of         Increase of the
   studied         roof glazing          of the roof         occupied hours         number of hours
                                          glazing             per year with        per year with Top >
                                                               Top > 28ºC                 28ºC
 Ref. Case              17                    20                  12.8                      0
 Case 2                21.3                   20                    13.5                    5.4
 Case 3                 17                    30                    13.3                    3.7
 Case 4                25.6                   20                    14.2                    11.2
 Case 5                29.8                   20                    15.0                    17.5



In the reference case (Table 8), the percentage of occupied hours with an operative temperature over
28 ºC lies by 12.8 %. In the case with an increased roof glazing surface from 17 to 21.3 % (case 2)
and the case using a roof glazing material with higher daylight transmittance (case 3), the effect on
the comfort conditions is limited: the augmentation of the number of hours of discomfort increases
respectively by 5.4 and 3.7 % which could be considered as acceptable.

A higher increase of the translucent roof surface up to 25.6 % and 29.8 % would be not acceptable
from the indoor comfort conditions point of view since it would represent an augmentation of the
number of hours of discomfort of 11.2 and 17.5 %, respectively.


4. Conclusions
A general assessment of the saving potential of the different measures has been compiled in table 10.

          Table 10: Evaluation of the energy saving potential of the different measures
          Energy saving measures                              Predicted energy savings
                                                   kWh      kWh/m2    % of total estimated demand
Warehouse lighting
Case 1pc Photocell control                      238,681       7.5                    18.5
           Increased roof glazing area
Case 2                                             47,736     1.5                     3.7
           (21,3 %)
Case 2pc Case 2 + photocell control             318,241      10.0                    24.7
           Higher transmittance of roof
Case 3                                             28,642     0.9                     2.2
           glazing
Case 3pc Case 3 + photocell control             289,600       9.1                    22.5


Daylight control with photocells constitutes an attractive alternative to reduce the energy consumption
of the building. This measures could contribute to reduce the electricity consumption of the whole
building by 18 %, corresponding to 238.7 MWh/a or 108.7 tons CO2/a (considering a CO2 emission
factor of 0.4556 kg CO2/kWh electricity).

Associated with an increase of the daylight penetration through an augmentation of the roof glazing
area from 17 % of the roof area to 21 %, savings of up to 24.7 % (318.2 MWh, 145 tons CO2/a) could
be reached without causing significant worsening of the summer comfort conditions.
The use of roof glazing materials with a higher daylight transmittance combined with daylight control
would represent savings of 22.5 %.

Additionally, the installation of a solar photovoltaic plant on the roof of the building is foreseen. This
plant with a nominal power of 261 kWp should produce almost 346 MWh/a electricity and would
represent an energy saving of 26.8 % of the total energy demand of the building.
By implementing a daylight control system, increasing the roof glazing area up to 21.3 % and
installing the planned photovoltaic plant it could be reached a primary energy savings of up to 51.5 %
corresponding to 664.2 MWh/a or 302.6 tons CO2/a.

If the use of roof glazing materials with a higher transmittance (30 %) is preferred instead of the
increase of the roof glazing area, a primary energy savings of 49.3 % could be reached corresponding
to 584.7 MWh/a or 266.4 tons CO2/a.

These measures would mean that the energy saving goals of the GreenBuilding programme would be
reached. However additional considerations on the economic viability of the measures are required.


Acknowledgement
The authors would like to acknowledge the collaboration of the technicians of Coperfil Inmobiliaria in
providing data for this work and the funding support of the project EIE/04/057/S07.38638 and
EIE/07/109/SI2.466268.


References
[1]   GreenBuilding website: www.eu-greenbuilding.org

[2]   Daylighting analysis software DAYSIM, http://irc.nrc-cnrc.gc.ca/ie/lighting/daylight/daysim_e.html

[3]   Tutorial on the Use of Daysim Simulations for Sustainable Design, Dr. Christoph F. Reinhart,
      Institute for Research in Construction, National Research Council Canada, Ottawa, Canada,
      2006

[4]   EnergyPlus website: http://www.eere.energy.gov/buildings/energyplus/

[5]   DesignBuilder website: http://www.designbuilder.co.uk/

[6]   Codigo Técnico de la Edificación, Documento básico HE – Ahorro de Energía, Sección HE3 –
      Eficiencia energética de las instalaciones de iluminación, 2006

[7]   GreenLight website: www.eu-greenlight.org

[8]   DAYSIM Case Studies, Dr. Christoph F. Reinhart, The Lighting Group – Institute for Research in
      Construction, National Research Council Canada, Ottawa, Canada, 2004

				
DOCUMENT INFO