www.dbdh.dk
N0. 3
2013
INTERNATIONAL MAGAZINE ON DISTRICT HEATING AND COOLING
DBDH - direct access todistrict heating technology
INTE
DHCSMART ENERGYNEW SOLUTIONS
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E N E R G Y A N D E N V I R O N M E N T
By Tarek Kim El Barky market manager for District Cooling, Rambøll Energy and Anders Dyrelund, senior market manager, Rambøll Energy
WHY DISTRICT HEATING ANDDISTRICT COOLING GO HAND IN HAND
More people prefer to live in cities. It is a challenge, but also
an opportunity to create more livable and sustainable cities.
We can provide the population with energy services in a
sustainable and cost effective way, if we in our urban planning
develop smarter energy systems and buildings. In order to do
that, it is important to focus on the interaction between the
most important elements of the energy system: The power
grid, the district heating grid, the district cooling grid, the gas
grid and not least thermal storages and building installations.
Several of these interactions are often attended, e.g. that
district heating (DH) is a precondition for efficient use of
surplus heat from CHP plants and renewable energy sources
(RES), and that the power grid can transfer the most cost
effective renewable electricity to the buildings compared to
building level installations.
But what about district cooling (DC)?
In this article, we will focus on DC, and how it in a smart way can
interact with the buildings and the rest of the energy system
and in particular DH.
WHY PLAN DH&C?
There are many good reasons why local governments and city
administrations should consider DH&C as a natural part of the
urban infrastructure.
In the EU, all cities are going to work with planning of DH and
DC:
• According to the Directive for Renewable Energy, local
governments shall consider if it is cost effective to transfer
renewable energy (RES) for heating and cooling via DH&C to
buildings compared to individual solutions
• Moreover, according to the latest directive for Energy
Efficiency, local governments have also to consider if it is
cost effective to develop DH&C in order to benefit from the
combined heat and power. In other words, DH and DC have
equal priority and go hand in hand in the planning.
• Finally, according to the directive for energy performance
of buildings, buildings shall have good indoor climate and
be “nearly zero carbon buildings” in a cost effective way
taking into account local conditions and the opportunity to
transfer RES and CHP to the buildings via DH and DC grids
Frederiksberg Forsyning proposes the
first cold water storage tanks in DK
FOCUSDHC
SMART ENERGY
NEW SOLUTIONS
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In all cities in the world, local governments may find that DH
and/or DC depending on the climate zone are vital parts of the
urban infrastructure, which should be integrated in the urban
planning for several reasons:
• The planning of the grids can be coordinated, e.g. by placing
DH and DC pipes in the same underground tunnels and
trenches taking into account other urban infrastructure
• The DH and DC plants, including thermal hot and cold water
storages, can be coordinated and located at suitable sites,
dedicated for technical installations and with the optimal
access to cooling facilities
• By interconnecting all buildings to the planned DH and DC
infrastructure where it is cost effective, the total costs for
thermal comfort will be reduced and the local environment
will be improved, e.g. as there will be no emission, noise or
visual pollution in city districts dedicated for human activity
– not least as the roof tops will be available attractive for
green gardens etc.
• The combination of DH&C grids and large hot and cold water
storages will significantly increase the ability of the energy
system to integrate fluctuating renewable energy sources
like wind and near-by low quality and low cost energy sources,
e.g. low temperature geothermal and free cooling
WHY SHOULD ENERGY COMPANIES DELIVER BOTH DH&C?
There are many good reasons for this combination:
• If the building owner needs both heating and cooling and
he is only offered one of these services, he might decide to
produce his own heating and cooling and benefit from the
synergy between them, e.g. an underground Aquifer Thermal
Energy Storage (ATES)
• If the building owner is offered both DH and DC, he will have
more available space on the roof and in the cellar and he will
save investments and operation costs
• As the energy company has professional staff and can
benefit from effects of scale, the energy company should
in principle always be able to give the building owner a good
competitive offer
• Even in case there is no DC or DH system yet, it could be
a good idea for the energy company to offer a temporary
“decentralized plant” to the building owner at a competitive
price
• In case the energy company owns and operates such a
decentralized plant within its natural district, before
the networks are in operation, the company has the best
opportunity to optimize and develop the DH&C networks and
maximize the connection rate
WHY SHOULD BUILDING OWNERS PREFER DH&C?
There are also many good reasons for this, e.g.
• Better economy via reduced capital and operating costs
• No need for own technical staff to operate a complicated
DH&C plant
• No noise from chiller
• Reduced risk of sudden repair costs
• No hazardous refrigerants in the building
• Easier and more cost efficient to certify the building with a
green certificate (such as LEED, BREEAM etc.)
• Available space on rooftop and basement for other purposes
• A greener company profile, due to less climate gas emissions
EFFICIENT BUILDING INSTALLATIONS FOR DH&C
The main task of DH &C systems is to use the available heating
and cooling sources in the city district, to provide thermal
comfort in buildings by stabilizing the indoor temperature
roughly between 20 and 25 dgr.C depending on the out-door
temperature. Energy efficient installations in the building,
which can use low temperature heat sources (e.g. at 30 dgr.C)
and high temperature cooling sources (e.g. at 15 dgr.C), will
significantly reduce network costs and open for opportunities
for energy efficient production of heating and cooling.
Such systems, e.g. floor tube systems for heating and cooling
combined with ventilation and eventual de-humidification and
small radiators, which can provide this high level of energy
performance in buildings, are already in operation.
An example is Ramboll’s office building in Kolding, which
improves the efficiency of the DH system and uses free cooling
at 15 dgr.C from a near-by stream.
Ramboll’s office in Kolding, Denmark, uses DHC and state-of-the-art
technologies to ensure a comfortable indoor climate.
Combined floor tubes and ventilation for heating and cooling in parallel
supplied by either district heating or free cooling.
DC RESPONDS EFFICIENTLY TO POWER PRICES
The traditional individual building level chillers are electric
driven. The main problem with individual chillers is that they are
uncontrolled and need to run continuous during the warmest
periods in order to provide the necessary comfort. Uncontrolled
chillers are the main reason for large investments in power
peak plants and even for blackouts in many cities around the
world. Large thermal capacity of buildings and small building
level cold water storages may reduce the peak demand a bit,
but it is an expensive solution and it takes up space. Provided
there is a certain cooling density in the city, a DC system based
on large electric driven compressor chillers and a large cold-
water storage is able to respond efficiently on the fluctuating
power prices. If necessary, all electricity consumption can
shift completely from daytime to nighttime. Moreover, the
necessary installed capacity in the centralized DC system is
significantly lower and more cost effective than the total of all
decentralized chillers, and the centralized cooling plant can be
connected to an efficient cooling source.
SURPLUS DH ENERGY FOR GENERATING DC
In some DH systems, there is a surplus of almost free heat
available at temperatures sufficiently to generate cooling by
absorption heat pumps, alone or in an optimal combination
with compressor chillers. The larger temperatures - the more
efficient production however, the lower temperature - the
more heat is available. A compromise between steam and low
temperature DH at temperatures below 100 dgr.C could be a
super-heated DH system with a maximal supply temperature
of 120-130 dgr.C.
The advantages of super-heated water compared to steam are:
• That the heat production from CHP will be more energy
efficient
• That more heat sources will be available, e.g. geothermal
• That the heat can be stored
• That the heat can be transmitted long distance
• That heat losses are lower
• That preinsulated pipes will be an alternative to the more
expensive concrete ducts
In case a free available heat source is available at e.g. 90 dgr.C,
it may be more cost effective to accept this temperature and
invest more in larger absorption chillers.
SURPLUS DC ENERGY FOR GENERATING DH
In some cases, the waste heat from the warm side of the
compressor chiller can be competitive for production of DH,
mainly to supply hot tap water – in case the temperature is
sufficient and there is a demand for it. One of the advantages
of DC in combination with DH is that the compressor is large
and that the warm side can deliver all the heat to the DH
system. The COP of the compressor chiller will be reduced as it
has to deliver heat at a higher temperature e.g. 70 dgr.C to the
DH system. Compared to the cooling tower however, the cost
of this will often be lower than the alternative production cost
of producing heat in the DH system. In any case, the surplus
heat from the chiller can be utilized if it is competitive.
One of the advantages is that the cooling plant does not need
a cooling tower or access to sea water or ground water if
it can rely entirely on the DH network and maybe a thermal
storage to absorb the surplus heat.
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E N E R G Y A N D E N V I R O N M E N T
WHY DISTRICT HEATING AND DISTRICT COOLING GO HAND IN HAND
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demand-side management
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As an example of the above, some of the largest DC systems
in Europe utilizes both sides of the chiller. In Stockholm, the
city has a DC capacity of 250 MW and delivers 440 GWh of
cooling every year. 75 % of the time, the condenser side of the
chiller is also delivering heat to the city. In Helsinki, cooling of
data centers delivers heat to the city. In Bjerringbro, Denmark,
a symbiosis between Grundfoss (a global pump manufacturer)
and the local DH company combines the need for cooling of the
production site with the need of heat for the city.
ATES FOR DH AND DC
In the Aquifer Thermal Energy Storage system (ATES), the
compressor is not cooled by the DH system, but cooled by the
ground water, which is pumped up from one well at e.g. 10 dgr.C
and injected in another well at e.g. 20 dgr.C. Thereby the ground
water around this well is heated during the summer. In winter it
is necessary to cool down the ground water for environmental
reasons.
This can be done using the same heat pump, as it in a reversed
operation can produce heat by cooling the ground water. The
ATES system is often installed at building level, but can as well
be installed in the interface between DC and DH system. The
advantages of using the ATES principle in a centralized way
instead of at the building level are:
• That the ground water wells may interfere in case each
building in a district has its own ATES system - a problem,
which has been recognized in e.g. Amsterdam
• That a centralized ATES plant can be located at a more
suitable location
• That the heat from the centralized ATES plant can be
produced in a more optimal way, taking into account both
heat production costs and power price hour by hour
• That the ATES capacity can be utilized more efficiently by a
DC system with cold water storage
Ground source cooling (at a high temperature)
GAS TO DC REDUCES POWER PEAK DEMAND
In modern cities in warm climates, some of the key problems
are “blackouts” or “brownouts” due to uncontrolled use of
decentralized air-conditioning. In some countries there is even
a power shortage or very high power prices for days. In such
systems, DC and cold water storages will improve the situation
significantly, but it may not be enough to reduce power peaks.
Therefore, the use of gas boilers and gas turbines to feed
the absorption heat pumps directly by steam or super-
heated water up to e.g. 160 dgr.C in peak periods is an obvious
opportunity.
In the city center of Tokyo, Tokyo Gas operates e.g. a 200 MW
district cooling plant heated by natural gas.
Natural gas can be stored in underground caverns or as LNG
and can therefore be important for the reliability of the power
system in hot summer days.
FUTURE PERSPECTIVES
In some countries, DH is the dominating heat source in cities,
whereas DC is almost unknown. In other countries, DH and DC
have very low market shares, although decentralized chillers
stress the power system and cause brownouts.
However, the DC market seems to be in transition from steady
to exponential growth. In recent years, many large companies
as well as legal and public authorities have gained interest in
this growing market. The potential benefits of DC are even
more interesting when DC is considered in combination with
the DH and the power system.
Regional, national and city authorities should therefore plan
for DH&C infrastructure as an integrated part of the urban
infrastructure whenever this is cost-effective in the longer
term taking environmental benefits into account. Thus, the
building owner will get the opportunity to meet “nearly zero”
carbon criteria in a cost-effective way by means of renewable
energy sources (free cooling) and efficiently combined heat
and power production via the DH&C grids. For utility companies
DC is expected to go from a “nice to have” to a “need to have”
service. By exploiting the optimization synergies with respect
to heat and cold production, the energy production of today
will be prepared for the smart livable energy cities of the
future, including efficient buildings and smart grids for power,
DH, DC and gas.
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www.dbdh.dk
Ramboll
Att.: Tarek Barky and
Anders Dyrelund
Hannemanns Allé 53
DK-2300 Copenhagen S
Phone: 45 5161 6680
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