HYDRAULIC BALANCE IN SMART HOMES

Using The KNX-standard for Performing Balanced Heating Conditions in

Dynamic Load Situations

Danny Szendrei, Tobias Teich, Susan Franke, Markus Schrader and Andre Worms

RG Integrated Information Systems, University of Applied Sciences Zwickau

Dr.-Friedrichs-Ring 2A, Zwickau, Germany

Keywords:

Energy-efﬁciency, Space heating, Dynamic hydraulic balance, Integrated building automation.

Abstract:

Efﬁcient and clean energy consumption is not only an essential request towards industrial economics. This

request also refers towards the residential building sector. There, the major share of energy consumption is

caused by house and facility heating. In Germany, most heating systems consist of double-pipe, hot water

systems. Due to the lack of hydraulically balanced system conditions, a potential of up to 15% energy-

savings can be assumed. This paper addresses the use of KNX-technology (Smart Buildings) in residential

buildings to ensure a dynamic adaption of hydraulic systems performance, in order to increase the heating

systems efﬁciency. Therefor, a procedure of heating system segmentation into hydraulically independent units

(meshes) is presented. This structure enables permanent control of adressable, net-based heating valve drivers

in order to achieve balanced mass ﬂow distribution over the whole facility. The dynamic hydraulic balance

is achieved by positioning these valves according to heating loads, that are generated from the temperature

settings in the corresponding rooms. The energetic advantages of single room heating control procedures,

based on the application FacilityManager, is presented.

1 INTRODUCTION

Providing sufﬁcient and clean energy is one of to-

days most challenging problems. Energy consump-

tion as well as production strategies are forced to be

aligned in many sectors. Facility management, resi-

dential housing, can contribute large potentials to de-

crease energy consumption. Thus, lower demands af-

fect sourcing and production strategies. About 50% of

the overall energy-consumption in Europe is caused

by buildings/facilities. A share of about 70% refers

to space heating. Thereby, the high share of out of

date buildings and heating systems highlights those

potentials. Invests in high efﬁcient heat generators

are deferred especially in the residential housing sec-

tor. Next to heat generation, the probabilities of en-

ergy savings in heat distribution systems are not used

adequately. In the future, the importance of hydraulic

balanced systems is expected to increase, due to tight-

ened legal restrictions (German Department Of Jus-

tice, 2009). Conventional hot water heating distribu-

tion systems, such as double-pipe-networks, are tech-

nically mature in most systems. Their long durability

delay important invests into modern hybrid systems.

Such heating systems are operated in about 70% of

all buildings in Germany. The highest share of those

systems lack hydraulic balanced operating conditions

(Guzek, 2010). These systems are an important op-

portunity for efﬁcency decreasing measures.

The after-effects of imbalanced systems are delayed

heat-up over the building, variable hydraulic condi-

tions, increasing energy consumption (primary and

secondary energy) and disturbing ﬂoating noises. In

simulations, FELSMANN and HIRSCHBERG found

out, that hydraulic imbalanced buildings cause 8%

higher mass-ﬂow-turnover than optimized buildings

(Felsmann and Hirschberg, 2007) and (N. Fumo and

Chamra, 2009). This additional turnover results in a

25% rise of electrical energy demand for the heating

turnover pumps.

The allocation of space heating in most build-

ings is achieved by conventional thermostatic heat-

ing valve drivers (thv) and circulation pumps. Al-

ternatively, thv can be replaced by motor valve

drivers, that recieve their actuating variable from ex-

ternal systems. Such systems are provided by KNX-

technology. KNX enables controlling local networks

in a variety of functions (power distribution, heat-

381

Szendrei D., Teich T., Franke S. and Schrader M..

HYDRAULIC BALANCE IN SMART HOMES - Using The KNX-standard for Performing Balanced Heating Conditions in Dynamic Load Situations.

DOI: 10.5220/0003409003810386

In Proceedings of the 8th International Conference on Informatics in Control, Automation and Robotics (ICINCO-2011), pages 381-386

ISBN: 978-989-8425-75-1

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

ing control, security installations and others). The

VPN-based bus integrates sensors and actors within

building networks and thus enables holistic control

procedures. Current room temperature control sys-

tems anticipate many environmental parameters and

self-adjust heat generator settings as well as heating

valve settings within the rooms. Caused by numer-

ous temperature settings through the users, the hy-

draulic conditions within a single pipe vary and inﬂu-

ence the proper hydraulic supply of remaining heating

devices within the same line (R.Yao and Steemers,

2005). Due to heterogeneous settings of different

users, conventionalmeasures of hydraulic balance fail

to compensate dynamic changes of difference pres-

sure, caused by the named reason. Via motor valve

drivers on each heating device, conﬁgurated within

bus structures, the valve settings can be used to com-

pensate these dynamics. As far as the hydraulic spec-

iﬁcations (i.e. difference pressures, characteristic di-

agrams of heating valves, valve driver ranges) of the

pipes are known, the valve positioning can be con-

trolled by a central facility server application. The

current value of the drivers enable information about

the hydraulic systems performance. Thus, different

load scenarios of the heating system can be consid-

ered in the controlling algorithms for each room in a

speciﬁc pipe and ensures dynamic hydraulic balance.

2 BUILDING SERVICES

For emphazising the potentials of integrated control

and automation systems, the current situation of facil-

ity management, with respect to heating systems, is

to be sketched. For presenting technical installations,

the following nomenclature is set:

Table 1: Nomenclature.

Symbol Meaning Unit

speciﬁc heat kJ/Kg · K

f energy coefﬁcent n.d.

valve range %

l length m

ν ﬂow velocity of water m/s

˙m mass ﬂow Kg/s

P pressure Pa

ρ (water) density Kg/m

Q primary energy W

˙q heat ﬂow density W/m

ζ pressure loss n.d.

2.1 Conventional Building Services

Building automation, especially Smart Home infras-

tructures, is only about to begin dispreading the mar-

ket. For about 10 years now, some applications for

detached houses have been developed and installed.

Volume services for residential buildings could not

be found among the retailers portfolios (T. Teich, M.

Zimmermann, S. Franke, F. Janh and M. Schrader,

2010). So far, most installations and their control

systems have been conducted by companies of differ-

ent crafts or branches and handicap integrative control

procedures. In the ﬁeld of heating, integrative build-

ing control was impossible to maintain, due to the fol-

lowing systems characteristics: Most heating systems

consist of the modules heat generation, heat distribu-

tion and heat transmission (Seifert, 2009). Heat trans-

mission appliances are structured according to the

dwelling unit structure. Due to heterogeneous heat

allocation, most heating systems work inefﬁciently

(Guzek, 2010) and appear most notably in large heat-

ing systems (Felsmann and Hirschberg, 2007). About

70% of residential buildings are equipped with central

heating systems with two-pipe installations (Guzek,

2010). Based on main heat distributing pipes (hor-

izontal), numerous rising pipes supply the rooms of

the buildings vertically. Each rising pipe distributes

the corresponding heating devices with mass ﬂow

of hot water and represents a single mesh. These

meshes mostly correspond with the vertical dwelling

unit structure. Within a mesh, the hydraulic condi-

tions vary according to: mesh-distance to circulation

pump; storey height; components parameters; room

utilisation. Within single dwellings, the user is capa-

ble to optimize utilisation towards cost-minimisation

and comfort-maximisation. These local optima inter-

fere and do not necessarily lead to an efﬁcient heat

supply over the meshes and the whole building. The

determinants of the efﬁciency are primary and sec-

ondary energy. It is important to understand the inter-

ference between the required energy of the used en-

ergy carrier (primary), and the necessary electrical en-

ergy for controlling and distributing (secondary) the

generated mass ﬂows, according to the equation:

∑

· f

(1)

Beside physical inﬂuences of the building (hull damp-

ing, internal heat transmission etc.), user settings

determine the primary energy demand signiﬁcantly

(N. Fumo and Chamra, 2009). Due to technical stan-

dards in conventional space heating systems, there is

a lack of information about user settings and their

effects (thermal and hydraulic) within the distribu-

tion system. Individual control sequences and thus

ICINCO 2011 - 8th International Conference on Informatics in Control, Automation and Robotics

382

mass ﬂow distribution are not aggregated for optimal

operation. Hydraulic balancing of the heating sys-

tems is often used to achieve more efﬁcient heat dis-

tribution. There are still about 90% of all operated

systems, where such measures have not been con-

ducted (Guzek, 2010) and (Szendrei, 2010). Stan-

dard procedures of hydraulic balancing cover hydro-

static adjustments for heating loads under extreme cir-

cumstances (full load). In this condition, the proper

mass ﬂow distribution can be obtained throughout the

system by adjusting proper resistance at the heating

valves (forward-motion pipe). Alternatively, resistors

are inserted in the backward-motion pipe of the dis-

tribution system. This adjustment is legally forced by

the DIN 18380 requirements. More realistic load pro-

ﬁles have to cover partial heating scenarios. In these

cases, that occur throughout 95% of the heating sea-

son, signiﬁcantly smaller mass ﬂows have to be cir-

culated by the distribution system. Besides meteoro-

logic inﬂuence, the mass ﬂow is object to dynamic

user settings (R.Yao and Steemers, 2005). That way,

the statically adjusted resistances are out of tolerance

and do not ensure homogeneous mass ﬂows. The ef-

fects of imbalanced working conditions are:

Thermal/Comfort Effects: delayed heat-up of

rooms/dwelling, ﬂow noises, declined control

quality of thv;

Efﬁciency Effects: increased energy demand, in-

creasing backward-motion water temperatures,

rising operating expenses, decreasing system

durability.

In order to achieve adequate hydraulic conditions,

the control system for space heating can be used.

To anticipate the hydraulic interferences between the

dwellings, it is essential to control the mass ﬂow of

each mesh that supplies different heating devices over

the storeys. Therefore, the conﬁguration of the KNX-

network must consider the systems installation of ris-

ing pipes and its attached devices. So far, mass ﬂow

speciﬁcations regarded the entire pipe setup within a

closed heating system according to:

˙m =

∑

· △ϑ

(2)

and

△p =

∑

(R·l)+

∑

(ζ·

· ρ

) (3)

Since smaller pipe sections are more simple to con-

trol and to calculate, such entire systems can be seg-

mented into meshes. Each rising pipe, supplying the

above storeys/rooms with water, may represent a sin-

gle mesh. At the main distributing pipe, a difference

pressure controler disconnects the meshes from the

hydraulic mainframe. The calculations and condi-

tions follow the shown procedures from equations 2

and 3.

2.2 KNX-based Building Services in

Space Heating

With these information, different load scenarios can

be modelled. A dynamic control within the given

structure with independent hydraulic mesh conditions

is enabled. Because of reducing the number of at-

tached heating valves, the mass ﬂow conditions are

to be assumed more effectively. Thus, possible load

scenarios can be modelled and deposited for facility

server applications. According to heating demand in

the meshes, valve ranges can be tuned in to dynami-

cally balance the meshes mass ﬂow and ensuring ad-

equate heat supply. The advantage of this approach

is the coverage of static and dynamic load proﬁles.

In general, heating valves in lower storeys require a

higher hydrostatic resistance (bigger valve range). In

accordance with the number of storeys, the necessary

resistance is to be decreased. The implementation of

this control requires accurately working valve drivers.

These are to be found among KNX-based, continu-

ously controlled drivers.

As demonstration and try-out objects, two multi-

storey residential buildings have been equipped with

KNX-based actors and sensors. Applications of

heating control, electric appliance control, protec-

tion/security control and others are installed. Besides

control procedures, the KNX-network enables visu-

alisation, remote operations, ﬂexible billing and in-

dividual setups of the installed components (T. Teich,

M. Zimmermann, S. Franke, F. Janh and M. Schrader,

2010). In the ﬁeld of heating control, the existing

building service hardware (i.e. heating devices, pipes,

heat generator) did not have to be renewed. The func-

tionality of heat generation and distribution hardware

was available for restarting it with KNX-based valve

drivers. Thus, integrative control procedures of room

temperature and heat generator settings are enabled

throughout the building. The valve drivers are ad-

dressable, continuously controllable units with a to-

tal range of 3 millimetres, that replaced the exist-

ing thermostatic valves. With such drivers, conven-

tional valve-cores became easy to control. Inside the

buildings, the equipment is linked via Ethernet. The

communication between facilities is transacted over

VPNs. Those provide a private communications net-

work over a shared public network infrastructure such

as the Internet. Basically, there are three types of

virtual private networks: Remote access VPN con-

nection (end-to-site), Branch Ofﬁce VPN connection

HYDRAULIC BALANCE IN SMART HOMES - Using The KNX-standard for Performing Balanced Heating Conditions

in Dynamic Load Situations

383

(site-to-site) and Extranet VPN connection (end-to-

end) (T. Teich, M. Zimmermann, S. Franke, F. Janh

and M. Schrader, 2010). The demonstration objects

are interconnected by a site-to-site VPN connection.

Regarding security issues, VPNs provide high protec-

tion against external access.

3 IMPLEMENTATION OF

SINGLE ROOM

TEMPERATURE CONTROL

3.1 Operational Description

Conceptual core of the heating control is maintain-

ing single room temperature control. This ensures

the appropriate comfort, required by the user. The

aim of the control is to harmonize the resulting dif-

ferences in mass ﬂow, that are caused by diverse,

interfering user temperature settings. KNX compo-

nents for single room control are a temperature sen-

sor, a heating actor and a heating device valve driver.

This setup refers to a single room with one heating

device (Szendrei, 2010). The desired set tempera-

ture is speciﬁed as a temperature proﬁle in the facility

server by the user. The value of the actual temperature

is compared to the set temperature value by the in-

stalled sensor via telegram-communication. Contrary

to thermostatic valve controls, the sensor is positioned

on the heating device facing wall. That is to pro-

vide pure values of the actual operating temperature.

As an offset for the single room temperature control

| ϑ

set

− ϑ

act

|≥ 0.5K has been adjusted. This offset

prevents the control system from oscillating (GIRA,

2006) and assures satisfactory thermal comfort for the

user (Guzek, 2010). The facility server based con-

troller tracks the actual temperature values of each

room by requesting KNXnet/IP-telegrams from the

devices. This communication is transacted full-time

in a two minute frequency. The exchanged informa-

tion is then used to measure the offset. In case of an

actual temperature being more than 0.5K lower than

the set value, a heating demand for the correspond-

ing room is generated. In such cases, a decision vari-

able HD is set true. According to the combinations

of heating demands within a mesh, speciﬁc load pro-

ﬁles and assigned valve ranges are deposited. Table 2

presents all possible heating load proﬁles and the as-

signed valve ranges for a dynamic hydraulic balance

in a three storey mesh (Szendrei, 2010).

According to the measured temperature offset,

HeatingDemand ist evaluated. The ranges for the

meshes valves are then assigned to the heating ac-

Table 2: Space heating load proﬁles within a valve mesh.

decision variabe HD valve range r

gnd ﬂ. 1st ﬂ. 2nd ﬂ. r

1st

2nd

0 0 0 0 0 0

0 0 1 0 0 100

0 1 0 0 100 0

0 1 1 0 75 100

1 0 0 100 0 0

1 0 1 75 0 100

1 1 0 75 100 0

1 1 1 65 75 100

tors and valve drivers via KNXnet/IP-telegrams. The

valve driver (re-) positions itself (corrective action)

and sustains that position until the next telegram re-

quest. During a control sequence, only one load pro-

ﬁle is valid. The valveranges are calculated on the ba-

sis of their speciﬁc character diagrams. From the dif-

ference pressure calculation (see section 2.1), the val-

ues of choking hydraulic resistance are known. Over

each mesh, these values can be expressed as ratios to-

wards the total difference pressure. Within a mesh,

each integrated valve produces an individual differ-

ence pressure. Thus, the corresponding ratios can be

used to determine the valve ranges, that create the re-

quired choking resistance, resulting from valve coef-

ﬁcients:

V·

1bar · ρ

△p

· 1000kg/m

/h] (4)

and

˙m = ρ ·

V [kg/h] (5)

According to the control frequency of two minutes,

the valve positioning assures a dynamic balancing of

mass ﬂow. That way, the hydraulic efforts of the

heating system can be reduced by about 8% (Guzek,

2010). Consequently, the secondary energy consump-

tion can be derated 25%, with regard to the simula-

tions of GUZEK. Those estimations are to analyse

by evaluating the heat ﬂow density within the dif-

ferent rooms in one mesh (Thron, 2001). Equal val-

ues thereby indicate proper hydraulic conditions. To

efﬁciently implement the control system with KNX-

based valve drivers, their metering characteristics are

to consider.

3.2 Metering Characteristics of

Available KNX-based Valve Drivers

For bus-based applications (KNX), different valve

drivers are available. Because of the requirements to-

wards high control quality for space heating, not all

ICINCO 2011 - 8th International Conference on Informatics in Control, Automation and Robotics

384

available drivers are suitable. To ensure effective, dy-

namic adaption of the heating device valve positions,

the parameters operating speed and control frequency

are to harmonize. As a matter of fact in residential

facility management, procurement, installation and

servicing costs have to be kept low and are used as

feasibility criteria. Reliable devices with the follow-

ing metering characteristics are available as thermal

drivers and electromotive drivers.

3.2.1 Thermal Valve Drivers

These discontinuously acting drivers usually work as

two-position controllers. Heating device valves can

be positioned to the opened and closed position (Zou,

2008). The control signal for the drivers is gener-

ated by the facility server. After its transaction to the

KNX-based heating actor, a voltage is triggered to the

driver. This voltage is used to heat-up a thermal re-

sistor, that devolves its extension onto the valve. This

technology is comparatively cheap. Major disadvan-

tage is the inaccurate controlling of the valve motion.

This is caused by the required heat-up time (t

− t

which is varying under certain circumstances. Fur-

thermore, the average heat-up time from two min-

utes exceeds the available cycle time of the control

procedure. Regarding these characteristics, accurate

valve positioning with two-position controllers seems

impossible. Another possibility is controlling ther-

mal valve drivers through pulse width modulation

(PWM). That modulation can be achieved by time-

dependent applying of voltage to the valve driver. The

pulsing periods have to consider heat-up as well as

valve motion duration, in order to maintain a virtual

continuous control. The modulation probabilities of

the virtual continuous controller require instant and

fast valve motions. Due to the components charac-

teristics, motions are delayed and unsteady. The aim

of dynamic and high frequency mass ﬂow adaption is

not to be implemented with the named drivers.

3.2.2 Motor Valve Drivers

Alternatively, electromotivevalve driverscan be used.

There are many suppliers who offer these drivers

with KNX-interfaces. The metering characteristic

of such components is continuous control. In gen-

eral, two control types are common. First: voltage-

proportional controllers. These drivers are supplied

with a voltage from 0.5 to 10 V. According to the ap-

plied level, the valve driver conducts a forward mo-

tion that is devolved onto the valve (Szendrei, 2010).

In addition to the bus cable, a power line has to

be installed for implementing this technology. Sec-

ond control type is a binary coded positioning sys-

tem within the drivers. A range recognition sys-

tem precisely positions the valve, according to the

incoming control signal. The signal is transmitted

via KNXnet/IP-telegrams. The telegrams contain a

two bit message, that represent the required valve set-

ting. Beside the accurate positioning capabilities, the

small effort for installation is to be highlighted. Only

bus cables are to be installed throughout the build-

ing. One disadvantage of this technology are higher

procurement costs. To achieve an optimal technical

infrastructure, the trade-off between metering charac-

teristics and procurement, installation and servicing

costs of the valve drivers had to be evaluated. Re-

garding the high controlling potentials of electromo-

tive driversand their higher durability,this technology

was chosen for implementation.

4 RESULTS

As a reference object, a multi-storey building with 18

dwellings has been equipped with KNX-technology.

Within the building, appliances of space heating, elec-

tromotive supply, presence detection, security and

others werde installed. The space heating is imple-

mented according to the shown concept. For the in-

stallation periphery, more than thirty single compo-

nents have been installed in every 2- or 3-bedroom

dwelling. Another dozen components assure the sys-

tems operation and control as centralized control de-

vices in the basements of the facilities. As a control

system, the application FacilityManager has been im-

plemented. This application detects and evaluates the

heating offset via temperatur sensors in a two-minute

frequency. The load proﬁles for range adjustment of

the heating valve by motor drivers were found accord-

ing to the valves characteristics. Since usage of space

heatings vary between the dwellings, identical heat-

ing scenarios were modelled. First evaluations of the

convergency of actual and set temperature values in-

dicate a uniform heat-up of the dwellings within the

meshes. More detailed analyses are to be carried out

in the upcoming heating season. Therefor, the differ-

ences in room-heat up have to be evaluated according

to:

˙q

hd,ref

· △t

hd,ref

· △t

ref

(6)

The density of heat ﬂow thus indicates hydraulic un-

dersupplies. As a reference (ref) for the homoge-

nous heat transmission, the heating devices (hd) in the

ground ﬂoors are assumed. This is caused by their

hydraulic advantaged location related to the above

installed devices. Furthermore, the electrical power

consumption of the circulation pump was measured.

HYDRAULIC BALANCE IN SMART HOMES - Using The KNX-standard for Performing Balanced Heating Conditions

in Dynamic Load Situations

385

In comparison to similar workloads, measured before

the systems renewal, ﬁrst savings could be detected.

For further proof, the circulation system will be com-

pared to a hydraulically non-balanced system with

similar parameters.

5 CONCLUSIONS

Energy savings, especially primary energy in space

heating, can decrease general energy consumption.

These large potentials are caused by the high share,

of improvable heating systems. In about 90% of these

buildings in Germany, heat distribution and transmis-

sion components lack hydraulic balanced operating

conditions. By launching smart building infrastruc-

tures, such as the KNX-standard, new control sce-

narios for various building services can be imple-

mented. The application of VPN-connected control

components enables hydraulic balancing while main-

taining single room temperature control throughout

(large) domestic buildings. To assure homogenous

mass ﬂow allocation, the heat distribution system was

segmented into hydraulically independent meshes.

Within each mesh, KNX-based heating valve drivers

are positioned in accordance to the corresponding

heating load proﬁle. The determination of load pro-

ﬁles is achieved by requesting actual temperature val-

ues via KNXnet/IP telegrams. The values from all

rooms are assigned to the speciﬁc mesh structure.

In different trials, electromotive valve drivers were

found to act most feasible while affording high dura-

bility. Such drivers are characterised by fast and pre-

cise range adaption. The installation effort for the pre-

sented infrastructureremains comparativelylow. First

energy savings, caused by hydraulic balanced heat-

up of the building, were measured at the circulation

pump. Because of the balanced hydraulic workload,

the electric energy consumption could be reduced.

Due to mild weather conditions, these savings in elec-

tric power consumption for the distribution system,

are to evaluate as initial estimations. High decom-

position measurements of the temperature spreading

(forward-backwardmotion) will indicate the homoge-

nous heat distribution over the meshes. These mea-

surements are initialized for the upcoming heating

season. Detailed calculations and utility analyses are

tasks for the further project work. Regarding the fea-

sibility of other building services, that have to be inte-

grated into the KNX-network technology, more ﬂexi-

ble and comfortable control procedures can be estab-

lished. For instance, the interference of light irradi-

ation, heating and ventilation can be integrated into

automated control scenarios for large facilities.

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