Danfoss Making applications future proof Application guide [zh]

District heating application guide

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+30

years of experience

in district heating applications, with more than 5 million installations worldwide.

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Structure

Recommended solution for heating systems / New construction 4

Recommended solution for heating systems / Renovation 6

1 Introduction 8

1.1 District Heating nets in China Yesterday, Today and Tomorrow 10

1.2 Common problems of the current District Heating systems in China and their causes 11

1.2.1 Heat losses in networks 11

1.2.2 Hydraulically unbalanced networks 12

1.2.3 Over specied pumps 14

1.2.4 Lack of centralized hot water treatment for DHW systems 14

1.2.5 General energy ineciency of the heat supply system 15

2 Connection to the grid 16

2.1 Central substation equipped by weather compensator, no controls in the building – direct connection of the buildings 16

2.2 Central substation equipped by weather compensator. Few buildings had Mixing units or substation at the entrance 18

2.3 Central Substations with mixing loops at each building or every connection 19

2.4 Substations in each building 20

2.5 Flat stations in each at for the same district 25

2.6 Conclusion 22

3 Direct connection of Heating system (connected via Central substations) 24

3.1 Mixing loop with Weather compensation and Combination valves for the Heating systems 21

3.2 Mixing-loop for Heating system, recommended than dP less than 2 bar 26

3.3 Mixing loop with 3-way valves to be used if the temperature in primary and secondary systems are equal 28

3.4 Mixing loop for Heating system with Weather compensation, Motorized Control Valves and Manual Balancing valves 30

3.5 Mixing loop for Heating system with Weather compensation and motorized control valves for the systems with

T in secondary side equal to T on primary side 32

4 Indirect connection of Heating system (Direct connection to the primary circuit) 34

4.1 Indirect connection of Heating system with DPC and MCV. DPC play also role of Flow limiter 34

4.2 Indirect connection of Heating system with DPCQ and MCV. DPCQ secure automatic ow limitation 36

4.3 Indirect connection of HE system with PIBCV 38

4.4 Indirect connection of HE system with MBV and MCV 40

4.5 Indirect connection of heating system with MCV only 42

5 Indirect connection of Heating and Domestic Hot water systems – directly to the primary side 44

5.1 Indirect connection of HE and DHW with common DPC 44

5.2 Indirect connection of HE and DHW with DPC on each circuit 46

5.3 Indirect connection of Heating and DHW system with DPCQ on each circuit 48

5.4 Indirect connection of HE and DHW systems with PIBCV used as control valve 50

5.5 Indirect connection HE and DHW systems with no DPC 52

5.6 Heating System connected thru Central substation via DPC on the entrance 54

6 Overall classication of Direct and Indirect Heating and Domestic Hot water 56

6.1 Direct heating system connection 56

6.2 Direct heating system connection 57

6.3 Domestic Hot Water Systems / Indirect DHW system connection 60

7 Product overview 62

7.1 Weather compensators - WC 62

7.2 Motorized Control Valves - MCV 62

7.3 Actuators for MCV and PICV 63

7.4 Pressure Independent Control Valves - PICV 63

7.5 Dierential Pressure (and Flow) Controllers - DPC (DPCQ) 64

7.6 Steel manual balancing valve and Ball valves 64

7.7 Temperature controllers 65

7.8 Energy meters 65

RECOMMENDED SOLUTION

Recommended solution for heating systems

RENOVATION

for heating systems

Source Distribution and

Transportation

CHP or Boiler house

Distribution station

Entrance of Building Raiser Entrance of

Mixing loop

DPC

Mixing loop

DPC Two pipe raise + TRV *** PIBCV+T One pipe raise + TRV ***

DPC MBV DPC ** Up to 6 oors Mixing loop MBV One pipe horizon + TRV **

DPC Mixing loop

Flat station DPC ** Mixing loop **

DPC

DPC ON/OFF CV * Up to 6 oors Mixing loop * Mixing loop Riser system * Flat station MBV One pipe raise + TRV *

In the Apartment Recommend index Note

Apartment

FH + RT ****

DPC

Two pipe horizon + TRV / FH + RT

***

MBV FH + RT *** PIBCV FH ***

Two pipe horizon + TRV

** More than 6 oors

/ FH + RT

PIBCV Horizon / FH **

** More than 6 oors

ON/OFF CV FH

** Up to 6 oors **

One pipe raise + TRV

FL One pipe horizon + TRV * ON/OFF CV with

preset

Horizon / FH * More than 6 oors

Recommend index

Introduction

With every day it becomes more and more obvious that energy eciency is one of the main trends in

the 21st century economic development. All branches of modern industry, from microelectronics to

heavy engineering, are striving to reduce energy losses. Today there is no other way: we may just go

forward or step aside of the progress.

This may seem incredible, but it is our unbounded household power inputs that cause the global

warming. In Europe, about 40% of fuel-energy resources are consumed by communal consumers,

while transport and industry consume 32% and 28% respectively. Notwithstanding the fact that

energy saving is an integral part of public policy of Western countries for many years. First of all,

this was favoured by the energy crisis which took place in 1970s and signicantly aected those

countries. Last year’s many of developed countries have achieved signicant results in this eld. In 25

years, they turned from consumers into suppliers of energy resources, rising to the rst places in the

world in energy eciency.

Index: 1980 = 100

180

160

140

120

100

Total energy consumption Heated area Energy consumption per m2

Figure 1:

Realizing that in future, high energy costs will be necessary to maintain high rates of growth, the

China Government has begun to implement a large-scale plan of radical increase of energy eciency

and decrease of fast-growing demand for coal from energy-consuming industries. For each level

of the government administration a target for decrease of energy consumption, which must be

achieved, is set. In addition to that, the Government has begun to implement a "large-scale program

of closing of ineective companies". Eorts, which China applies, striving to raise its energy ecien-

cy, are probably the most resolute ones among those that have been ever applied in this eld by any

country. They will be discussed for years. But in spite of this trend there are several other problems,

for example, in heat-power engineering, particularly concerning heat distribution. Unfortunately,

the current condition of heat networks is far from the ideal, while it is not possible to carry out the

necessary replacements instantly. In this book, the main issues will be discussed and solutions,

related to Danfoss, its equipment and experience, will be proposed.

1.1

District Heating nets in China Yesterday, Today and Tomorrow.

Connection of the building to the grid designed at 80ths old constructed District heating systems with network

structure as presented on the pic. 2 still have a high presence on the market.

Distribution

station

Building sub-

Source

station

Figure 2: District heating network

A brief overview of old District Heating Nets can be characterized by following:

• Weather compensated temperature control only at the heat source (combined heat power plants, boiler

installations)

• High level of heat losses

• High cola consumptions

• High demand for better water treatment

• Constant ow in primary and secondary circuits.

• Overspecied pumps

• Excessive consumption of heat and electric power

• Lack of comfort conditions for end-users

• High return temperature on Primary Side

• Hydraulic unbalance

• Energy ineciency

Domestic hot water system (DHW)not-connected to the District heating system and prepared by electrical /gas

boiler. In the regions Solar panels also used for DHW systems

1.2

Common problems of the current District Heating systems in China and their causes.

1.21

Heat losses in networks

Generally, the heat networks has been designed and constructed in 80s years of the last century. Since then

constant economic growth and industrial development required continual construction of new networks, while

the old ones practically were not reconstructed. Total heat losses reach ~ of the consumer heat load.

It is possible to distinguish two components of heat losses:

Heat losses

Leakage

Figure 3: Type of heat loses

Losses due to leakages:

This issues caused by all-round wearing of the heat networks. Corrosion makes holes in pipeline walls, bad seal

Loses from surface -

non insulated

in valves and between ange connections, which results in leaks.

Losses from pipeline surfaces:

Heat network pipelines are made of steel, which is an excellent thermal conductor. As it can be seen from the

following expression, this type of losses depends on a number of factors; among those are thermal conductivity

of the material and the dierence between the external air and the heat carrier temperatures.

Q =λ· (t1– t2) · F.

Lack of insulation, as well as the heat carrier temperature in the supply pipe, which is as high as 130 C, results in

heat losses of ~ Gcal per m

Insulation of the pipeline and decrease of the operating parameters allows lowering the losses down to ~ per

1 running meter

Conclusion:

Total heat losses reach 273 million Gcal per year, which amounts to 34.745 billion RMB in cash equivalent.It is

impossible to solve the issue by mere replacement of pipelines: this will require huge manpower,

material and time resources. Measures, which can be taken now, are reduction of the temperature

curve and all-round insulation of pipelines. This will signicantly reduce the heat losses and grant

additional time, required for gradual reconstruction and replacement of heat networks.

1.22

Hydraulically unbalanced networks

Present-day heat supply systems of residential, production and administration buildings are con-

nected to heat networks via central substations. Consumer heat loads are unstable and, as a result of

quantity and quality regulation, which takes place at the heat source. This is a serious issue obviously

take place in heavily branched heat networks, due to their unbalance. Function of limitation of

maximal heat carrier ow by end consumer is also quite hard to implement.

Currently, hydraulic balancing of a heat network is carried out at the design conditions by means of

throttling orices or, at the best, by means of manual balancing valves or circulating pumps with

variable frequency converters. Resistance of the latter can be calculated by the following expression:

However, it is impossible to achieve balance between the quantity and quality regulated heat

network and consumers by means of the throttling devices, because as the ow changes from G1

to G2, hydraulic resistance of an orice or a manual balancing valve, which have constant hydraulic

characteristics (Kv), changes as square of the ow.

ΔРа ΔРb

ΔРc ΔРd

Figure 4: Standard piezometric diagram

Orices and manual valves can be used for balancing in systems with constant ow only. Quantity

and quality regulation in heat networks balanced by means of these devices results in oating piezo-

metric curve and, as a consequence, variable local pressure drops at building connection.

Similarly, usage of circulating pumps with variable frequency converters does not meet the expectations laid

on it. Indeed, total pressure of an unbalanced network does not change; excessive pressure and ow (which are

built up locally as the result of operation of automatic equipment and local decrease of the heat carrier ow)

are simply redistributed to the nearest objects. Thus variable frequency driving actuators do not perform their

primary function

ΔРа

ΔРb ΔРc

ΔРd=0

Figure 5: Piezometricschedulefor peakheat loadsperiod

Existence of the oating piezometric curve makes it impossible to limit the maximal ow by means of orices

and manual balancing valves. Limitation of maximal ow, as well as hydraulic balancing of systems with varia-

ble ow can be carried out by means dierential pressure controllers only. Such controllers are capable to main-

tain the stable pressure drop in the regulated variable ow system. In case of increase of the input pressure they

ensure stable limitation of the maximal heat carrier ow. With usage of such controllers, "internal" hydraulic

balancing of heat networks at every central substation and building substation is no longer required. Orices

and manual balancing valves can be removed from pipelines: balanced distribution of the heat is achieved due

to additional hydraulic resistance of the DP controllers located at heat stations in each building.

Dismissal of quarterly balancing of heat networks invalidates the piezometric curve (there is no more local loss-

es at orices and manual balancing valves), the former "problem" objects receive local pressure drop required

for their operation. In centralized thermal supply systems these measures lead to signicant economic eect.

Circulation pumps of the heat networks instantly obtain the required pressure. Such heat power reserves make

it possible to connect additional consumers to the existing networks without considerable capital costs.

ΔРа ΔРb ΔРd

ΔРc

Figure 6: The reduction of the circulationowinheating systems

1.23

Over specied pumps

Another important issue, which requires attention, is over specied pumps installed at the heat

source thermal chambers and central heat supply stations. What is the reason of this problem? Why

does it have an negative inuence? The pumps are selected in assumption that the most distant

consumer must receive the heat carrier at the maximal ow, i.e. taking into account the maximal

hydraulic resistance. As the result, consumers located closer to the heat source or the central heat

supply station experience signicant "harmful" pressure, which must be decreased (wasting of

energy). Large safety factors stipulated by the network design are also not always useful. An over

specied pump operates in non-optimal conditions, which lowers its eciency (ref. the gure

above), increases electric energy consumption, decreases the life-time and heightens the noise level.

Currently, more and more systems are transferred to dynamic model of operation, and installation of

variable frequency converters becomes a requirement. If it is not possible to replace the pump itself,

the frequency converter will maximally optimize its operation in various operating modes.

In addition to all the mentioned above, usage of Overspecied pumps results in increase of capital

and operating costs.

1.24

Lack of centralized hot water treatment for DHW systems

Currently, only local water heaters installed directly in consumers' buildings are used. This results not

just in increased consumption of electric energy and gas, which can be used much more eectively.

It is well known that heating is not needed in summer, and the corresponding network pipelines are

drained. As the result, internal pipe surface contacts with air, which speeds up corrosion in several times, which,

in turn, ruins leak-proofness of the pipes and increases heat losses resulted by leaks.

1.25

General energy ineciency of the heat supply system

All the above mentioned issues make a common image of the situation. Unfortunately, it is necessary to state

that the heat supply system stays generally inecient in spite of the eorts being applied. Renewal and recon-

struction of the large-scale systems require huge amounts of resources: time, money, manpower. Besides, the

problems of the heat supply system aect the allied industries:

Electric power industry (additional loads: water heaters in buildings, pump driving actuators)

Mining operations (additional loads: fuel for combined heat power plants and boiler installations)

Objective set by the Government of China is real and achievable. The future and economy of the country

depends on achievement of this objective. Yes, the capital costs are relatively high, however, in 5 - 10 years

benets of the modernization will signicantly exceed this value and open new horizons of development.

Danfoss has capabilities, experience and complete solutions which solving these issues. Some solutions,

described below, are widespread in Europe and also in Russia. Advantages of Danfoss' solution is:

• Decreased environmental impact,

• Energy saving,

• Decreased pay-back time,

• Improved comfort for tenants.

2.1

Connection to the grid

Central substation equipped by weather compensator, no controls in the building – direct connec-

tion of the buildings

Weather Compensation

One of the solution,

Weather compensated temperature control at the heat source (combined heat power plants, boiler

installations)

• Weather dependent temperature control at central substations

• Local temperature control: thermostats installed on end consumers' radiators

• Variable ow in primary and secondary circuits.

• Manual balancing valves at building connections

• Domestic hot water system not connected to the District heating system and prepared by electri-

cal /gas boiler. In the regions Solar panels also used to control the water

The main disadvantage of such model is that the consumer is provided with sucient amount of

heat only in case the necessary specications of the network and the heat source are precisely met

and constant (because consumers are unable to adjust ow and, consequently, temperature)

Such model could be deemed viable earlier, prior to total upgrade of heat sources, Heat networks

and heating systems. However, usage of such models gets more and more undesirable. Consumers

and the Heat network experience almost all the problems mentioned above, like:

• Excessive consumption of heat and electric power

• Excessive temperature of the returning heat carrier

• Hydraulic unbalance

• Energy ineciency

• High rates of corrosion in the summer months

2.2

Central substation equipped by weather compensator. Few buildings had Mixing units or

substation at the entrance

Weather Compensation

The second case is inseparably linked with progressive partial automation of buildings and end users, which,

as it was mentioned in section 1, threatens the whole system. Weather compensators close and open valves

in order to achieve the conditions conformable for the user. If such consumers become too large in number,

the other consumers become aected. Consumers not equipped with automation or even Dierential pressure

controllers may face with the following diculties and problems:

• Increase of pressure in return pipelines

• Pressure oscillation

• Overheating of premises

• Insucient heating

2.3

Central Substations with mixing loops at each building or every connection

Weather Compensation

For the renovation of the District Heating Nets, one of the compromised solutions might be installation in each

building the mixing loops for Heating system with keeping the Central Substations for the group of buildings.

Temperature and heat controlled based on the weather compensation principle to the consumer (right in the

building) compare to the previous solutions. Thus lead to increased energy-eciency and energy savings on the

level of 15-20%.

PICV or combination of DPC + MCV secure the hydronic stability, ow limitation and reduce the risk for cavita-

tion and pressure oscillations in the system. Needles to mark that by using DPC, hydronic stability achieved as

for primary as for secondary sides.

2.4

Substations in each building

Weather Compensation

HEX

Indirect connections are used regardless of pressure value in the point of connection to the Heat network, which

means that such models are versatile. Hydraulic insulation between the heating systems and the Heat network

signicantly raises reliability of thermal supply systems, protects local systems from increase and decrease of

pressure in the Heat network, and allows keeping water in the heating system in case of emergency, because it

is prevented from freezing due to circulating pumps operation..

For consumer benets are:

• Comfort parameters due to the weather compensation

• Stable and accurate controls of parameters as in on the secondary as on primary sides

• Independence of system from other buildings

• HIGH energy eciency – for heat and for electricity

• HIGH energy savings – up to 25%

2.5

Flat stations in each at for the same district

Icon of Flat station

The decentralized heating system comprises an installation, for which at stations built into each apartments

that are supplied from a central energy source. These units normally incorporate a compact plate heat ex-

changer, which delivers instantaneous DHW on demand and a dierential pressure control valve to control the

heating ow to the tenants’ radiators or oor heating.

The essence of decentralized heating systems is in moving certain processes from the central substation to the

individual ats.

In order to secure optimum system performance of the at station it is important to dimension the system

correctly. A dimensioning tool provided by Danfoss provides an easy way for correctly dimensioning the at station.

Ref: eFlat dimensioning tool at danfoss.com

Decentralized systems can operate with all available energy sources. The most frequently used are either an

indirect DH substation, any other directly connected substation or boiler installation. All the sources can be

combined with solar.

The benets of having a at stations compared to traditional systems include

• Accurate individual energy metering

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