Energy Efficiency Project Analysis for Supermarket and Arenas

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					                  ENERGY EFFICIENCY PROJECT ANALYSIS
Training Module   FOR SUPERMARKETS AND ARENAS
SPEAKER’S NOTES   CLEAN ENERGY PROJECT ANALYSIS COURSE


                  This document provides a transcription of the oral presentation (Voice & Slides) for this training
                  module and it can be used as speaker's notes. The oral presentation includes a background of project
                  considerations and provides an overview of the RETScreen Model. The training material is available
                                                   ®
                  free-of-charge at the RETScreen International Clean Energy Decision Support Centre Website:
                  www.retscreen.net.


                  SLIDE 1: Energy Efficiency Project Analysis
                           for Supermarkets and Arenas

                  This is the Energy Efficiency Project Analysis for
                  Supermarkets and Arenas Training Module of the
                  RETScreen Clean Energy Project Analysis Course. In this
                  presentation, we examine advanced approaches to                                               Slide 1
                  refrigeration and energy efficiency in supermarkets and
                  arenas.



                  SLIDE 2: Objectives

                  This module has three objectives. First, to review the
                  basics of advanced refrigeration systems and energy
                  efficiency measures for supermarkets, ice rinks (arenas),
                  and curling rinks. Second, to illustrate key considerations
                  in energy efficiency project analysis for supermarkets and                                   Slide 2

                  arenas. And third, to introduce the RETScreen Energy
                  Efficient Arena and Supermarket Project Model.



                  SLIDE 3: What do efficiency measures and advanced
                           refrigeration systems provide?
                  The ensemble of measures discussed in this presentation
                  target the provision of refrigeration, cooling, space
                  heating, ventilation air heating, water heating and
                  dehumidification in supermarkets and arenas. While this                                      Slide 3
                  is their raison d’être, they are associated with a range of
                  secondary      benefits,     including   reduced     energy
                  consumption, reduced power demand charges, reduced
                  refrigerant leaks, reduced greenhouse gas emission,
                  reduced maintenance costs, and improved occupant
                  comfort.
               RETScreen® International




SLIDE 4: Supermarkets:
         Background

Supermarkets use more energy per unit area than most commercial buildings. A large
supermarket will consume 5,000 MWh of electricity per year, and there are over 5,000
such large supermarkets in Canada. Together, this represents electricity consumption of
around 25 TWh per year, or the output of about three large power plants.                       Slide 4

Refrigeration systems typically account for around 50% of a supermarket’s energy costs,
and lighting around 25%; in terms of energy consumed, these figures would be slightly
lower. This translates into $150,000 per year in energy costs for refrigeration in a large
supermarket. To put this in context, energy costs are equivalent to roughly 1% of
supermarket sales. This is very significant, considering that the average net profit margin
for a supermarket is also approximately 1%. That means that all other things being equal,
a 10% reduction in energy costs increases profits by about 10%!
So supermarkets, and their refrigeration systems in particular, are major consumers of
energy, and the cost of providing this energy strongly influences store profitability. But
there is another aspect of supermarkets that merits attention: they are also responsible
for the release of large quantities of the greenhouse gases linked to global climate
change.
Supermarket greenhouse gas emissions stem not just from the production of the energy
they consume, but also from leaked synthetic refrigerant. Conventional supermarket
refrigeration systems contain very large refrigerant charges: an average large store will
have 1,300 kg of refrigerant. This refrigerant circulates in long piping runs connecting
display cases, distributed around the supermarket, to the mechanical room. These long
piping runs, with their joints and connections, permit annual leakage of 10 to 30% of the
refrigerant charge. Because synthetic refrigerants are potent greenhouses gases, with
many having over 3,000 times the effect of carbon dioxide, the leaking refrigerant of a
typical large supermarket is equivalent to the greenhouse gas emissions of 100 to 200
cars and light trucks.



SLIDE 5: Arenas:
         Background
Ice rinks (arenas), which for this presentation comprises skating rinks and curling rinks,
are major consumers of energy. A typical skating rink, were it to use only electricity,
would consume around 1,500 MWh per year; in reality, many rinks use natural gas to
provide some of this energy. Curling rinks use around one quarter to one half as much
                                                                                               Slide 5
energy as skating rinks, in part because they require less frequent ice resurfacing. As
shown by the pie chart on this slide, refrigeration, heating, and hot water together
account for around 75% of the energy consumed by the rink; refrigeration alone uses
about 45%. The annual cost of providing energy to a skating rink is around $100,000; this
is a significant expenditure for the municipalities operating these facilities.
In Canada, there are roughly 2,300 skating rinks and 1,300 curling rinks. These consume
around 4 TWh of energy annually; were it to be provided solely in the form electricity, this
would be equivalent to the output of several moderate-size power plants.
Ice rinks (arenas) release significant quantities of greenhouse gases. This arises not just
from the production of the energy consumed by the rink, but also from leaked synthetic
refrigerant. Conventional ice rink (arena) refrigeration systems contain very large
refrigerant charges: an average skating rink will have 500 kg of refrigerant. The use of
open compressors results in significant leakage. Because synthetic refrigerants are
potent greenhouses gases, with many having over 3000 times the effect of carbon
dioxide, these leaks result in serious greenhouse gas emissions.
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SLIDE 6: The building as a system


When attempting to reduce the energy consumption, power demand, and environmental
impacts of a supermarket or ice rink (arena), it is helpful to think about the building as a
system. Supermarkets and ice rinks (arenas) can be described as systems requiring
purchased energy inputs, such as electricity and natural gas, to satisfy simultaneous, or            Slide 6
nearly simultaneous, heating and refrigeration loads. In this, they are similar to many
other buildings. Their distinguishing characteristic is that the heating and refrigeration
loads occur in warm and cold zones that are in close proximity, such that heat from the
warm zone can drain into the cold zone. For example, in a supermarket refrigerated
display cases will line an aisle where the air should be kept around 20ºC, and in an ice
rink (arena) stands at, say, 15ºC will overlook an ice surface at –6ºC.



SLIDE 7: Heating and refrigeration loads

Within the supermarket or ice rink (arena) building “system”, a number of heat gains and
losses influence the total heating and refrigeration load. In common with other buildings,
these include gains from and losses to the environment, occupants, equipment, and
processes. As in other buildings, reducing the unwanted portion of these gains and
                                                                                                     Slide 7
losses is one avenue to energy efficiency. But in supermarkets and ice rinks (arenas),
these gains and losses are often minor in comparison to the heat transferred from the
warm zone to the cool zone. This is, therefore, an even richer vein of potential energy
savings.



SLIDE 8: Where are improvements possible?


As suggested by the preceding analysis of the building as a system, energy savings,
decreases in power demand charges and reductions in environmental impact can be
achieved through a number of approaches. Perhaps the easiest is to decrease the
energy requirement by controlling lighting and temperature according to building activity,           Slide 8
occupancy, and environmental conditions. Then heating and refrigeration loads can be
tackled by reducing the heat transfer from the warm to cold zones and decreasing other
unwanted gains and losses, as in other buildings.
Having reduced the amount of heat and refrigeration that must be supplied, measures
that supply this in a more intelligent way can be implemented. Here very significant
savings can be achieved through “process integration.” That is, viewing the building as a
system, the heating and refrigeration systems are integrated such that the heat withdrawn
from the cool zone is used to heat the warm zone, rather than being dumped to the
environment.
Incremental energy savings will result from the use of more efficient heating, ventilation,
air conditioning, and refrigeration equipment. On the other hand, certain equipment
choices can radically reduce the refrigerant charge and leakage, resulting in enormous
reductions in greenhouse gas emissions.
In the following slides, we will examine some specific measures, starting with the ones
that are most widely applicable and having the most impact. But first, a quick review of
the vapour compression cycle at the heart of most refrigeration equipment.




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SLIDE 9: Review of vapour-compression refrigeration cycle


Most refrigeration equipment in supermarkets and ice rinks (arenas) relies on the vapour-
compression refrigeration cycle. In this cycle, heat is extracted from a cold zone and
rejected to a warmer zone.
                                                                                               Slide 9
The evaporator is a heat exchanger that is in contact, directly or indirectly, with the cold
zone. A flow of cold refrigerant, mostly in the liquid state, passes through the evaporator.
Since the refrigerant is even colder than the temperature of the cold zone, heat flows
from the cold zone into the refrigerant. This heat causes the liquid refrigerant to
evaporate; its temperature changes little, however.
The gaseous, low pressure and low temperature refrigerant exits the evaporator and then
passes into a compressor, typically driven by an electric motor. The compressor
drastically raises the refrigerant’s pressure and, as a consequence, its temperature.
The high temperature, high pressure gaseous output of the compressor is then fed into a
second heat exchanger, called the condenser, where heat is extracted. The refrigerant
entering the condenser is warmer than the air or heat transfer fluid on the other side of
the condenser, so heat flows out of the refrigerant. As it loses heat, the refrigerant’s
temperature drops somewhat and it condenses.
This high temperature liquid refrigerant then passes through an expansion valve. The
valve reduces the pressure of the refrigerant, and as a result, its temperature falls. This
low temperature liquid is then fed into the evaporator, and the cycle repeats.



SLIDE 10: Supermarkets and Arenas:
          Problem: Heat transfer from warm to cool zones

As explained in earlier slides, the heat lost from the warm zone to the nearby cold zone is
a major energy flow in many supermarkets and ice rinks (arenas). In fact, it usually
accounts for the majority of the refrigeration load in these buildings. In conventional
refrigeration systems, heat flows in an “open loop”: it is furnished to the warm zone by the   Slide 10
heating system, lost to the cool zone, extracted by the refrigeration system, and then
dumped to the outside air by the condenser. Thus, much of the heat being rejected to the
outside air was provided by the heating system, and the heating system must supply an
equivalent amount of heat to the warm zone to make up for this loss.
Because the heating load for the warm zone is mainly caused by losses to the cold zone,
in supermarkets and ice rinks (arenas) the heat rejected by the refrigeration system will
nearly always exceed the heating load. The energy supplied to the refrigeration system,
as well as heat gains to the cold zone from the occupants, the environment, and
equipment, add to the quantity of rejected heat, and result in a surplus, compared to the
heating load.
This is illustrated by this graph showing heat load and rejected heat for a typical
Canadian skating rink. During every month, the refrigeration system rejects heat in
excess of the heat load. Although during winter, there may be periods of days or even
weeks when there is a net demand for heat. For supermarkets, the surplus of rejected
heat is even more pronounced, and the rejected heat will, in many cases, always exceed
the heat load, at least on a daily basis.




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               Energy Efficiency Project Analysis For Supermarkets and Arenas Training Module




SLIDE 11: Measures for Supermarkets and Arenas:
          Process Integration makes use of heat rejected by refrigeration system

Since, as discussed in the previous slide, the heat rejected by the refrigeration system
will generally exceed the heating load, why not make use of it and reduce the
consumption of energy for heating purposes? In short, why not “close the loop” and return
the heat extracted from the cold zone back to the warm zone whence it came?                           Slide 11

This can be achieved by capturing heat from the refrigeration system in a “secondary
loop,” or closed loop circulating a heat transfer fluid that is in thermal contact with but
otherwise isolated from the refrigeration system’s refrigerant. It is possible to recover the
heat rejected by the refrigeration system without using a secondary loop, but the
secondary loop facilitates the distribution of heat to the various heat loads, and, as will be
seen in the next slide, is environmentally advantageous.
The rejected heat is recovered at the outlet of the compressor. One fairly conventional
technology, already in use in some supermarkets and ice rinks (arenas), is a
desuperheater. The compressor normally raises the temperature of the refrigerant above
that at which it evaporates; the desuperheater extracts heat but only in quantities that
keep the refrigerant at temperatures above where it will condense. Since these
temperatures are fairly high, a desuperheater is good for generating hot water. It recovers
only around 15% of the heat that must be rejected, however.
Further heat exchangers downstream of the desuperheater can recover the remainder of
this heat. Since this will cause the refrigerant to condense, the temperature of this
extracted heat is fairly low. Nevertheless, it can serve for space heating, ventilation air
heating, and further water heating. If necessary for a particular application, a heat pump
can raise the temperature of heat available from the secondary loop.
The heat rejected by the refrigeration system will generally be in excess of that required
for heating loads. If the building includes heat storage, this excess can be stored for later
use, as will be discussed in upcoming slides. In ice rinks (arenas), the heat can be
productively used to heat under the ice rink (arena) slab, thus preventing the ground from
freezing and heaving, or can be used for melting the snow pit. In both supermarkets and
ice rinks (arenas), the heat can be exported to nearby buildings for heating purposes, or
used to heat sidewalks, parking lots, or streets, thus keeping them free of snow and ice in
winter. Any surplus that remains can be dumped to the outside air.
In the figure on this slide, the red loop indicates the secondary loop on the condenser
side of the refrigeration system. Heat is recovered from the loop by heat exchangers
shown to be within the mechanical room. If there is heat in excess of the demand, it is
rejected to the environment.



SLIDE 12: Measures for Supermarkets:
          Minimize refrigerant leaks with secondary loops
Supermarket refrigeration loads are typically distributed around the building. In a
conventional system, long loops of piping filled with synthetic refrigerant connect these
loads to the mechanical room, and further loops connect to the condenser. Leaks in the
joints and connections of these pipes account for 50% of the supermarket’s greenhouse
                                                                                                      Slide 12
gas emissions.




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SLIDE 12: Measures for Supermarkets:
          Minimize refrigerant leaks with secondary loops (cont.)

These emissions can, therefore, be drastically reduced by the use of cold and hot
secondary loops. In the place of synthetic refrigerant, these loops contain water, a glycol
mix, brine, carbon dioxide, methanol, or some other heat transfer fluid that has low or no
global warming potential. Synthetic refrigerant is still used by the refrigeration system, but
it is contained in a hermetic unit with a minimal refrigerant charge, located in the
mechanical room.
The figure on this slide shows the condenser side secondary loop in red, as before, and
the evaporator side secondary loop in blue. The latter loop circulates a suitably cold heat
transfer fluid between the low temperature display cases and the refrigeration system.
For very low temperature loads, such as freezers, two approaches are possible. One is to
use two or more cold-side secondary loops, each operating at a different temperature.
Another is to use autonomous refrigeration sub-units, contained within the freezers
themselves, that reject their heat to a cold-side secondary loop that is nevertheless not
cold enough for direct use in the freezer. This permits heat recovery and good efficiency
while isolating the small refrigerant charge within the freezer.



SLIDE 13: Measures for Arenas:
          Minimize refrigerant leaks with secondary loops

In conventional ice rink (arena) refrigeration systems, an open compressor circulates hot
refrigerant in a loop linking it to the condenser, which will normally be located at some
distance from the mechanical room. Leakage of the resulting relatively large charge of
synthetic refrigerant causes significant greenhouse gas emissions.
                                                                                                 Slide 13

These emissions can be greatly reduced by isolating the synthetic refrigerant in a
hermetic unit located in the mechanical room; rejected heat is transported away from the
unit in a warm side secondary loop containing water, a glycol mix, or some other heat
transfer fluid having little or no global warming potential. The refrigerant charge is
minimized, leaks are reduced, and heat distribution is facilitated.
The figure on this slide shows the condenser side secondary loop in red and the
evaporator side secondary loop in blue. Heat is rejected from the former and cooling is
transported to the ice slab with the latter.



SLIDE 14: Measures for Supermarkets and Arenas:
          Tailoring HVAC&R equipment to cold climates

Much of the refrigeration equipment installed in cold climate supermarkets and ice rinks
(arenas) was designed for warm climates. In particular, equipment designers assumed
that the outside air temperature would be high, so the condenser rejects heat at a high
temperature. To achieve these high temperatures, unnecessary in cold climates for most
of the year, the compressor must work hard to pressurize the refrigerant to the required
level. This increases energy consumption and shortens the lifetime of the compressor.




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               Energy Efficiency Project Analysis For Supermarkets and Arenas Training Module




SLIDE 14: Measures for Supermarkets and Arenas:
          Tailoring HVAC&R equipment to cold climates (cont)

Now equipment is available that permits “floating head pressure:” the compressor raises
the pressure and temperature of the refrigerant only to the level necessary for heat
rejection. During cold weather, the coefficient of performance can double, from 3 to 6, for
example, and less energy is consumed per unit of cooling provided. The compressor
operates at lower pressures for much of the year, and suffers less wear.
Note that when the heat rejected by the refrigeration system is used for heating purposes,
it will be less useful as its temperature drops. Additional energy will be consumed to
supplement or upgrade the rejected heat. Thus, as shown by the figure on this slide, the
combined refrigeration and heating load is minimized at a certain condensing
temperature, even though the refrigeration system would be more efficient at lower
condensing temperatures. The choice of condensing temperature thus becomes an
optimization problem dependent on the heating load, refrigeration load, and outside air
temperature.



SLIDE 15: Measures for Supermarkets and Arenas:
          Mechanical/ambient refrigerant subcooling

In typical supermarket and ice rink (arena) refrigeration systems, the liquid exiting the
condenser at the condensing temperature feeds directly into an expansion valve.
Subcooling, a technique for improving capacity and efficiency, involves inserting a heat
exchanger between the condenser and the expansion valve, and cooling the refrigerant                 Slide 15
well below its condensing temperature. For the same mass flow rate of refrigerant, and
thus the same work done by the compressor, more refrigeration is achieved.
There are two approaches to extracting this additional heat. Ambient subcooling relies on
cold outside air or, in the case of an ice rink (arena), the snow pit. For example, if the
condensing temperature is 25ºC—warm enough for the heat in the secondary loop to be
useful—but the outside air is at 0ºC, it is possible to subcool the refrigerant by around
20ºC. Without any additional compressor work, refrigeration equivalent to the sensible
heat of a 20ºC drop in the refrigerant temperature occurs.
The second approach, mechanical subcooling, uses a small, second refrigeration system
to subcool the refrigerant. An obvious question is why such a second refrigeration system
should be any more efficient than simply running the primary refrigeration unit a little
more. The answer lies in the temperatures at which these two systems operate: the
difference in the condenser and evaporator temperatures will be much smaller in the
subcooling unit, so it can operate with a higher coefficient of performance than the
primary system.



SLIDE 16: Measures for Supermarkets and Arenas:
          Thermal storage

While the heat rejected by the refrigeration system will typically exceed the heat load on a
monthly or even, in the case of supermarkets, daily basis, there will be short periods
when the instantaneous heating load exceeds the rejected heat. This may be the case,
for example, on very cold nights. Rather than operating a dedicated heating system for               Slide 16
these periods, heat can be stored during times of surplus and withdrawn as needed. Not
only does this reduce energy consumption, but it can also reduce peak demand charges
in those areas where they are levied.

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SLIDE 16: Measures for Supermarkets and Arenas:
          Thermal storage (cont.)
Short term and long term storage is possible. Hot water, stored in tanks totalling
2,000 litres or so, can affordably provide storage sufficient for several hours of heating.
The ground can be used for long term storage, including transfers from summer to winter.
A buried horizontal or vertical ground heat exchanger extracts or rejects heat to the
ground as necessary, as shown on this slide; the long distance to the surface and poor
conductivity of the soil retain the heat in the vicinity of the heat exchanger.
Ice rinks (arenas) can also store cold, generated during times of moderate or low
refrigeration load, under the concrete slab or in a reservoir. Then, during peak
refrigeration loads, cold is withdrawn from storage, reducing the load on the refrigeration
equipment. Where they are levied, power demand charges may be decreased, and
equipment of lesser capacity can be installed.
Storage permits a heat pump to simultaneously generate heating and refrigeration with
the same energy input, increasing the effective coefficient of performance. Consider an
ice rink (arena) operating at a point in time—for example, at night—when the refrigeration
load is low, and thus when rejected heat is in deficit of the heating load. A heat pump can
extract heat from the cold storage in order to meet the heat load. The next day, during
higher refrigeration loads, the cold storage will provide more cooling, due to this
withdrawn heat, and the refrigeration equipment will operate less.



SLIDE 17: Measures for Supermarkets and Arenas:
          Efficient lighting and daylighting
Artificial lighting consumes energy twice. First, to make the lights come on, and second,
to remove the heat that the lights generate. The augmentation of the refrigeration load is
particularly severe in ice rinks (arenas). More efficient lighting technologies are, therefore,
an attractive way to reduce energy consumption.
                                                                                                  Slide 17

There are additional ways to reduce lighting energy consumption, however. Artificial
lighting requirements can be reduced by around 30% through the use of highly reflective
ceilings. In ice rinks (arenas), aluminized materials with low emissivity, discussed in the
next slide, achieve this purpose. Furthermore, controls can reduce lighting intensity
according to the activity and occupancy. Ideally, this involves the use of lamps that can
operate at multiple intensity levels. The number of operating lamps can also be varied,
although care must be taken to avoid dark spots objectionable to occupants. A careful
study may reveal that, when ceiling and wall reflectivity are taken into consideration,
optimal placement of the lighting fixtures, and even lowering of the ceiling, permit further
reductions in artificial lighting.
Another option, creating an ambience pleasing to the occupants, is the use of natural
lighting, as seen in the photo on this slide. Compared with artificial lighting, natural
lighting generates less heat per unit of light, reducing the refrigeration load. But attention
must be paid to avoiding glare, excessive heat gains and losses through windows and
skylights, and unwanted solar gains, especially the admittance of direct solar radiation.




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               Energy Efficiency Project Analysis For Supermarkets and Arenas Training Module




SLIDE 18: Measures for Arenas:
          Ceilings that radiate less heat

The ceiling of an ice rink (arena) tends to be quite warm—certainly at a temperature in
excess of the ice surface. Heat emanating from artificial lighting and space heating of the
stands tends to rise to the ceiling and raise its temperature; with poorly insulated ceilings,
solar radiation on the roof also exerts a strong influence. A conventional ice rink (arena)
                                                                                                       Slide 18
ceiling surface, of wood or steel for example, will have a high emissivity index, perhaps
0.80 to 0.95, indicating that it radiates heat very well. Thus, the warm ceiling radiates heat
to the ice surface and is responsible for up to 30% of the ice sheet refrigeration load.
Installing a ceiling with a low emissivity, or “low-e”, surface can reduce the heat radiated
from the ceiling to the ice surface. Low-e aluminized cloth has an emissivity of 0.03 to
0.08, meaning that at the same temperature, it radiates only one-thirtieth to one-tenth as
much heat as a conventional ceiling material. Alternatively, aluminium-based low-e paint
or other low-e paint can achieve reasonably low emissivity indices.
Low-e ceilings have advantages beyond reduced ice sheet refrigeration load. Because
the ceiling radiates less heat, it stays warmer and less condensation forms on the ceiling
structure. Acoustics are often improved and, as mentioned in the previous slide,
aluminized cloth ceilings are highly reflective, reducing artificial lighting requirements. The
photo on this slide shows such a ceiling.



SLIDE 19: Measures for Arenas:
          Reduce heat losses from stands
Because the spectator stands of an ice rink (arena) are adjacent to the cold ice surface,
space heating of the stands, especially by forced hot air systems, tends to add to the
refrigeration load. The air temperature in the stands may be as high as 15 to 18ºC—over
twenty degrees higher than the ice surface. This heat migrates from the stands to the
                                                                                                       Slide 19
refrigerated zone, adding 20% to the refrigeration load. The image on this slide shows
simulated ice rink (arena) air temperature, with blue indicating cold and red hot, as
heated air rises from the stands to the ceiling; it should be noted that the configuration
shown here, with higher walls around the ice surface, was designed to minimize heat
transfer to the ice.
Using low temperature radiant slab heating can minimize the heat loss from the stands.
This involves circulating a heat transfer fluid at, say, 32ºC or lower, in a piping network
embedded in the floor and sometimes even the seats. The low temperature of the heat
and limited rate of heat transfer from the slab to the air decreases heat losses to the ice
surface. Furthermore, it is possible to use the low temperature heat rejected by the
refrigeration system for this purpose. Best of all, warm radiant floors and seats are
exceedingly comfortable: spectators feel warm, even when air temperatures are low.
Simply reducing the temperatures in the stands will also reduce heating and refrigeration
energy consumption. During unoccupied periods, this will have no impact on spectator
comfort.




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SLIDE 20: Measures for Arenas:
          Optimize ice temperature

Most ice rinks (arenas) keep the ice temperature constant, at around –6ºC, throughout
the day and throughout the season. Permitting the ice temperature to vary depending on
occupancy and occupant activity can reduce the energy consumed in refrigeration. For
example, during figure skating, the system can be set to keep the ice at –3 to –4ºC, and          Slide 20
during free skating, this can rise to –2 to –3ºC. During unoccupied periods, the
refrigeration system and secondary fluid pump can be stopped; they need be restarted
only when an infrared sensor indicates that a preset maximum temperature — -1 to -2ºC
for instance — has been reached. Letting the ice temperature rise and stopping the
secondary fluid pump reduce energy consumption.



SLIDE 21: Measures for Arenas:
          Reduce refrigerant pumping energy

The ice in an arena is cooled by the circulation of a cold secondary fluid in the concrete
slab under the ice. Conventionally, a “two pass” layout is used: that is, a piping network
transports the secondary fluid across the ice in one direction and then back to the header
in the opposite direction. A constant speed pump forces the secondary fluid through this          Slide 21
network. This pump often accounts for over 15% of the energy consumed by the
refrigeration system; furthermore, the work done by the pump heats the secondary fluid,
adding to the refrigeration load.
There are two approaches to reducing the energy consumption of the secondary fluid
pump and thus the refrigeration load. One is to reduce the secondary fluid flow rate
according to a schedule, with, for example, lower flow rates at night. This can be
achieved through the use of a two-speed pump, two separate pumps, or a variable speed
pump. A second approach is to use a multi-pass piping network, such that the fluid
makes four or more passes across the slab before returning to the header. Multipass
layouts can halve the secondary fluid flow rate, reducing pumping power and the
refrigeration load. The refrigeration system design will need to be adjusted to
accommodate the reduced flow rate. Some people question the uniformity of the ice
surface with a multipass layout, but it has been implemented successfully in a number of
rinks.



SLIDE 22: Measures for Arenas:
          Optimize ice and concrete slab thickness
The secondary fluid circulating in the slab must be at a temperature low enough to result
in heat transfer sufficient for the surface of the ice above it to be kept at a certain desired
temperature. Thicker ice or a thicker layer of concrete above the embedded piping
network reduces the heat transfer from the secondary fluid to the surface, forcing the
                                                                                                  Slide 22
refrigeration system to work harder.
In most arenas, the ice is 25 to 40 mm thick, but in some ice rinks (arenas) with uneven
slab surfaces, thickness approaches 75 mm. Ice rinks (arenas) generally embed the
secondary fluid piping network with approximately 25 mm of concrete above the tubes,
but there is some variation in this as well.




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               Energy Efficiency Project Analysis For Supermarkets and Arenas Training Module




SLIDE 22: Measures for Arenas:
          Optimize ice and concrete slab thickness (cont.)

To ensure that heat transfer to the ice surface is not impeded, attention should be paid to
maintaining the ice at its minimum acceptable thickness and, during construction or
renovation, keeping the concrete layer above the secondary fluid tubes at 25 mm or less.
In certain jurisdictions, regulations will dictate the minimum acceptable ice thickness;
elsewhere, the ice should be 25 mm thick.
These measures can reduce the required capacity of the refrigeration system, particularly
when used in conjunction with under-slab cool storage. The cool storage moderates
temperature swings in the slab, reducing peak refrigeration loads; this is especially
important if thinner slabs, with less thermal mass, are used.



SLIDE 23: Measures for Arenas:
          Different dehumidification approaches

To prevent excessive condensation on the ice and within the rink, arenas normally
employ a stand-alone dehumidification unit. These devices, which must cool the air below
its dew point in order to remove the humidity, typically reject their heat to the ice rink
(arena) interior air. This adds to the load of the primary refrigeration system.                   Slide 23

An alternative that can reduce overall rink energy consumption is to reject the heat from
the dehumidifier to the condenser-side (that is, the warm side) secondary loop of the
principal refrigeration system. Then the rejected heat can be used for space heating,
water heating, or other purposes.
Another approach is desiccant dehumidification, which utilises a material that chemically
or physically absorbs water vapour. Such materials are often used in a cycle of
absorption and “regeneration”, during which a source of heat drives the absorbed water
out of the material. In the past, high temperature heat, such as produced by gas
combustion was required for regeneration, but recently desiccants that can be
regenerated at low temperatures have begun to appear.



SLIDE 24: Supermarkets:
          Costs of efficiency measures
The cost of implementing efficiency measures in a supermarket will depend on the
package of measures applied. Certain measures, such as night time setbacks of lighting
and temperature, may be implemented at essentially no cost. A full package of process
integration, secondary loops, and other measures may cost 40% more than comparable
                                                                                                   Slide 24
conventional approaches. For a large Canadian supermarket, this might add $250,000 to
the cost of construction or major renovation. While these measures can generate
significant savings, supermarket owners and operators demand quick paybacks, often
around 3 years or less. The net initial costs decrease, and therefore the simple payback
improves, if the integrated heating and refrigeration system eliminates the need for a
dedicated combustion heating system.




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SLIDE 25: Arenas:
          Costs of efficiency measures

Ice rinks (arenas) require a major renovation roughly every 25 years. An integrated
heating and refrigeration system with a warm side secondary loop and other major
efficiency measures will typically add $175,000 to the cost of a single pad renovation and
$200,000 to the cost of a multipad renovation. For comparison, the total cost of such a            Slide 25
renovation might be around $700,000.
Rink owners and operators typically demand a simple payback period of 5 to 8 years. An
integrated heating and refrigeration system with secondary loops has a 3½ year payback
in new construction, and a 5 to 8 year payback as a retrofit.
Efficiency measures that require only minor investments include better controls for
lighting and temperature, the use of night time setbacks, and the optimisation of ice
thickness. Desuperheaters, dehumidification, snow pits, and electrical power factor
correction (not discussed in this presentation) require a moderate investment of capital.
Measures requiring a major investment of capital, and having paybacks typically in
excess of five years, include low emissivity ceilings, efficient lighting, multipass circulation
of secondary fluid, refrigerant subcooling, fully integrated heating and refrigeration
systems with secondary loops, floating head pressure, and thermal storage.



SLIDE 26: Supermarkets:
          Project Considerations

There are a number of considerations particular to the implementation of energy
efficiency projects in supermarkets. Paramount among these is the need for a system
with proven reliability. This is key when unconventional technologies are being promoted:
the cost to the supermarket of even a one day failure of their refrigeration system is very        Slide 26
high, and decision-makers are risk averse as a consequence.
Efficiency measures requiring moderate or major investments will be most attractive
when incorporated into new construction or major equipment overhauls. Fortunately,
supermarket refrigeration systems are overhauled every 8 years on average, providing
numerous opportunities for improvements and the introduction of new technologies.
Supermarkets operate year round, without a convenient shutdown period during which
equipment can be upgraded. It must be possible, therefore, to install and bring on-line
new refrigeration systems and efficiency measures without interrupting regular
supermarket activities.
A large supermarket’s refrigeration system typically rejects heat in excess of the heating
load throughout the year. A simple and convincing argument for an integrated heating
and refrigeration system is the possibility of entirely eliminating combustion heating.



SLIDE 27: Arenas:
          Project Considerations
There are a number of considerations particular to the implementation of energy
efficiency projects in ice rinks (arenas). Among these is the long period between arena
overhauls. Efficiency measures requiring moderate or major investments will be most
attractive when incorporated into new construction or during major equipment overhauls,
                                                                                                   Slide 27




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               Energy Efficiency Project Analysis For Supermarkets and Arenas Training Module




SLIDE 27: Arenas:
          Project Considerations (cont.)

but a rink need be overhauled only every 25 years. On the other hand, 30 to 40% of
Canadian rinks are presently operating beyond their projected life span, so there are
significant opportunities for improvements. Many arenas close for one or two months
during the summer, facilitating retrofits.
A typical ice rink (arena) refrigeration system rejects, on an annual basis, three times the
rink’s requirements for heating. This bodes well for integrated heating and refrigeration
systems. In Canada there are, however, periods of days or weeks during winter when the
heat load may exceed the rejected heat. These are the key design conditions for the
system.
In some Canadian provinces, electricity tariffs include charges for the maximum power
demanded by a consumer. These peak power demand charges can account for as much
as 40% of electricity costs in an arena. In these provinces, the power demand reduction
associated with an efficiency measure should be considered.



Slide 28: Example: Quebec, Canada
          Repentigny supermarket

The Loblaws supermarket in Repentigny, just northeast of Montreal, is a 10,000 m2
showcase of energy efficiency measures. Secondary loops are used on both the cold and
warm sides of the refrigeration system. The medium temperature refrigeration system
rejects heat to a loop providing up to 250 kW of space and air heating. The low                     Slide 28
temperature refrigeration system provides up to 220 kW of heat, upgraded by heat pumps
that can serve as air conditioners if so required. A desuperheater supplies the building’s
hot water. Mechanical subcooling is used on the low temperature refrigeration system,
with the subcooling provided by the medium temperature refrigeration system secondary
loop. In addition, the head pressure, and therefore the condenser temperature, is
adjusted in response to the building heating requirements and the outside air
temperature.



Slide 29: Example: Quebec, Canada
          Repentigny supermarket (results)

The concept of using heat rejected by the refrigeration system to fully meet the
supermarket’s heating needs is proven by the simple fact that the Repentigny Loblaws
has no combustion or backup heating system. On-going monitoring points to reductions
                                                                                                    Slide 29
in energy consumption of around 20%, and reductions in greenhouse gas emissions of
around 75%. Greenhouse gas emissions reductions stem not just from reduced gas
consumption, but, more importantly, from reduced refrigerant leaks. The system started
without a glitch, required minimal commissioning, and has operated trouble-free since
April 2004.




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Slide 30: Example: Quebec, Canada
          Val-des-Monts recreational ice rink

The recreational skating rink in Val-des-Monts, northeast of Ottawa, contains a wide
range of measures addressing the building’s energy consumption and environmental
impact. The heating, ventilation, and air conditioning system are tightly integrated, with
the heat rejected by the refrigeration system recovered in a secondary loop. This             Slide 30
provides low temperature radiant heating for the building and, through upgrading via a
heat pump, service hot water and resurfacing water. Rejected heat is also used for under
slab heating, snow pit melting, and excess can be stored or used for heating in a nearby
community centre.
The system incorporates three types of thermal storage: a 2,000 litre hot water reservoir
and under pad cold storage operate over the short term, and a horizontal, closed loop
ground heat exchanger makes use of the ground for seasonal storage.
Two measures minimize the energy used to pump the secondary coolant. First, a
five-pass, rather than two-pass, layout is employed. Second, six cascaded 3 horsepower
pumps achieve variable secondary coolant flow rates in response to the slab refrigeration
demand.
The refrigeration system is designed for Val-des-Mont’s cold climate: floating heat
pressure permits the condenser temperature to drop when it is cool outside. A highly
reflective, low emissivity ceiling is complemented by optimally situated, highly efficient
lighting; artificial lighting of 10.5 kW is thus sufficient where a conventional rink would
require lighting of 25 kW.



SLIDE 31: Example: Quebec, Canada
          Val-des-Monts recreational ice rink (results)

The measures installed in the ice rink (arena) achieve significant cost savings for the
municipality of Val-des-Monts and drastically reduce the building’s greenhouse gas
emissions. Energy consumption is 60% lower than that of a Canadian model building
code reference rink. This is illustrated by the figure on this slide comparing energy         Slide 31
consumption at Val-des-Monts to the average energy consumption of 40 comparable
Quebec ice rinks (arenas) over the course of the winter of 2001 and 2002. The Val-des-
Monts rink has 50% lower peak power demand than the average Quebec rink; annual
savings in energy costs and power demand charges total $60,000.
The use of sealed refrigeration units and secondary loops permitted the rink to use only
36 kg of synthetic refrigerant where a typical rink would use 500 kg. The result is a
greater than 90% reduction in greenhouse gas emissions compared to a typical rink.
Furthermore, the synthetic refrigerant that was used does not impact the ozone layer.
No special skills are required for autumn rink start-up and end-of-season shutdown, so
outside contractors need not be called in unless required by law. Radiant slab heating of
the spectator stands makes the Val-des-Mont rink exceptionally comfortable.




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               Energy Efficiency Project Analysis For Supermarkets and Arenas Training Module




Slide 32: RETScreen® Energy Efficient Arena & Supermarket Project Model


The RETScreen Software estimates the energy savings, life-cycle costs, and greenhouse
gas emissions reductions for supermarkets and ice rinks (arenas), permitting the user to
investigate the impact of a wide range of advanced efficiency measures. These include
the integration of the refrigeration and heating systems in order to achieve waste heat            Slide 32
recovery, the use of secondary loops to distribute heat while reducing refrigerant leakage,
lighting and ceiling improvements, floating head pressure, varying the thickness of the ice
and layer of concrete above the embedded tubes, and other measures discussed in this
presentation. The RETScreen Software permits the use of multiple currencies, operates
in a choice of unit systems, and includes a number of useful auxiliary tools.



SLIDE 33: Conclusions


Supermarkets and ice rinks (arenas) are major consumers of energy. This presentation
has shown that cost-effective energy efficiency measures and improvements to
refrigeration systems in arenas and supermarkets can greatly reduce energy
consumption and greenhouse gas emissions. Through process integration, heat rejected               Slide 33
by the refrigeration system can satisfy most or all of a supermarket’s or arena’s heating
load and, in certain cases, even eliminate the need for combustion heating systems.
RETScreen calculates the energy savings and greenhouse gas emissions reductions
associated with a wide range of energy efficiency measures and refrigeration system
improvements for supermarkets and ice rinks (arenas). In so doing, RETScreen provides
significant preliminary feasibility study cost savings.



SLIDE 34: Questions?


This is the end of the Energy Efficiency Project Analysis for Supermarkets and Arenas
Training Module of the RETScreen Clean Energy Project Analysis Course.

                                                                                                   Slide 34




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