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

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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

tke@ramboll.dk

ad@ramboll.dk

For further information please contact: