Danfoss Making applications future proof Application guide [zh]

District heating application guide

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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 specified pumps	14
1.2.4 Lack of centralized hot water treatment for DHW systems		14
1.2.5 General energy inefficiency 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 flat 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

3.5Mixing 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

2

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 flow 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 classification 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	Differential 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

3

RECOMMENDED SOLUTION for heating systems

Recommended solution for heating systems

NEW CONSTRUCTION

Source	Distrubution/	New construction:	Raiser	Entrance of
	transporatation	Entrance of Building		Apartment
		Substation		Flat station
	Distribution station
		Substation		DPC
	Distribution station	Mixing loop
		Substation	DPC
	Distribution station			DPC
		Substation		PIBCV
Heating
		Mixing loop		PIBCV
source
			DPC
	Distribution station			MBV
		DPC
				PIBCV
		Substation
	Distribution station	Mixing loop	DPC	ON/OFF CV

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	In the Apartment	Recommend index	Note
	Two pipe horizon + TRV / FH + RT	*****
		*****
	Two pipe horizon + TRV / FH + RT	****
	FH + RT	****
	Two pipe raise + TRV	****
	Two pipe horizon + TRV	***
	Horizon / FH	***
	FH	***
	Two pipe raise + TRV	***
	Two pipe horizon + TRV / FH + RT	**	More than 6 floors
		**	Up to 6 floors
	Horizon	**
	Horizon / FH	**
	FH	**
	Horizon	*

Recommend index

5

RECOMMENDED SOLUTION for heating systems

Recommended solution for heating systems

RENOVATION

	Source	Distribution and	Entrance of Building	Raiser
		Transportation
			Mixing loop
			Mixing loop	DPC
				DPC
				PIBCV+T
				DPC
			DPC
			Mixing loop
	CHP or Boiler	Distribution station
				DPC
	house		Mixing loop
				Flat station
			DPC
			Mixing loop
				DPC
			DPC
			Mixing loop
			Mixing loop
			Flat station	MBV

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		Entrance of	In the Apartment	Recommend index	Note
		Apartment
			FH + RT	****
		DPC	Two pipe horizon + TRV	***
			/ FH + RT
		MBV	FH + RT	***
		PIBCV	FH	***
			Two pipe raise + TRV	***
			One pipe raise + TRV	***
		MBV	Two pipe horizon + TRV	**	More than 6 floors
			/ FH + RT	**	Up to 6 floors
		MBV	One pipe horizon + TRV	**
		PIBCV	Horizon / FH	**
		ON/OFF CV	FH	**	More than 6 floors
				**	Up to 6 floors
				**
			One pipe raise + TRV	**
				**
		FL	One pipe horizon + TRV	*
		ON/OFF CV with	Horizon / FH	*	More than 6 floors
		preset
		ON/OFF CV		*	Up to 6 floors
				*
			Riser system	*
			One pipe raise + TRV	*

Recommend index

7

1 Introduction

With every day it becomes more and more obvious that energy efficiency 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 significantly affected those

countries. Last year’s many of developed countries have achieved significant results in this field. In 25 years, they turned from consumers into suppliers of energy resources, rising to the first places in the world in energy efficiency.

180	Index: 1980 = 100
160
140
120
100
80
60
40
20
0

Total energy consumption		Heated area		Energy consumption per m2

Figure 1:

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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 efficiency 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 ineffective companies". Efforts, which China applies, striving to raise its energy efficiency, are probably the most resolute ones among those that have been ever applied in this field 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.

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	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
Source	Building sub-
	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 flow in primary and secondary circuits.

•Overspecified pumps

•Excessive consumption of heat and electric power

•Lack of comfort conditions for end-users

•High return temperature on Primary Side

•Hydraulic unbalance

•Energy inefficiency

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

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	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			Loses from surface -
			non insulated
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 in valves and between flange 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 difference 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 m2

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

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		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 significantly 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 flow 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 orifices 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 flow changes from G1
		to G2, hydraulic resistance of an orifice or a manual balancing valve, which have constant hydraulic
		characteristics (Kv), changes as square of the flow.

b

c

d

D

Figure 4: Standard piezometric diagram

Orifices and manual valves can be used for balancing in systems with constant flow only. Quantity and quality regulation in heat networks balanced by means of these devices results in floating piezo-

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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 flow (which are built up locally as the result of operation of automatic equipment and local decrease of the heat carrier flow) are simply redistributed to the nearest objects. Thus variable frequency driving actuators do not perform their primary function

b

c

d=0

D

.

Figure 5: Piezometric schedule for peak heat loads period

Existence of the floating piezometric curve makes it impossible to limit the maximal flow by means of orifices and manual balancing valves. Limitation of maximal flow, as well as hydraulic balancing of systems with variable flow can be carried out by means differential pressure controllers only. Such controllers are capable to maintain the stable pressure drop in the regulated variable flow system. In case of increase of the input pressure they ensure stable limitation of the maximal heat carrier flow. With usage of such controllers, "internal" hydraulic balancing of heat networks at every central substation and building substation is no longer required. Orifices 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 losses at orifices 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 significant economic effect. 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.

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1.23

1.24

b

c

d

D

Figure 6: The reduction of the circulation flow in heating systems

Over specified pumps

Another important issue, which requires attention, is over specified 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 influence? The pumps are selected in assumption that the most distant consumer must receive the heat carrier at the maximal flow, 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 significant "harmful" pressure, which must be decreased (wasting of energy). Large safety factors stipulated by the network design are also not always useful. An over specified pump operates in non-optimal conditions, which lowers its efficiency (ref. the figure 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 Overspecified pumps results in increase of capital and operating costs.

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

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		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 inefficiency 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 inefficient in spite of the efforts 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 affect 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 benefits of the modernization will significantly 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.

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2	Connection to the grid

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

Weather Compensation

16

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 flow 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 electrical /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 sufficient amount of heat only in case the necessary specifications of the network and the heat source are precisely met and constant (because consumers are unable to adjust flow 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 inefficiency

•High rates of corrosion in the summer months

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	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 affected. Consumers not equipped with automation or even Differential pressure controllers may face with the following difficulties and problems:

•Increase of pressure in return pipelines

•Pressure oscillation

•Overheating of premises

•Insufficient heating

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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-efficiency and energy savings on the level of 15-20%.

PICV or combination of DPC + MCV secure the hydronic stability, flow limitation and reduce the risk for cavitation and pressure oscillations in the system. Needles to mark that by using DPC, hydronic stability achieved as for primary as for secondary sides.

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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 significantly 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 benefits 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 efficiency – for heat and for electricity

•HIGH energy savings – up to 25%

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2.5	Flat stations in each flat for the same district

Icon of Flat station

The decentralized heating system comprises an installation, for which flat stations built into each apartments that are supplied from a central energy source. These units normally incorporate a compact plate heat exchanger, which delivers instantaneous DHW on demand and a differential pressure control valve to control the heating flow to the tenants’ radiators or floor heating.

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

In order to secure optimum system performance of the flat station it is important to dimension the system correctly. A dimensioning tool provided by Danfoss provides an easy way for correctly dimensioning the flat 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 benefits of having a flat stations compared to traditional systems include

• Accurate individual energy metering

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