WP3.D5 Recommendations for Concepts for Easy Installation and

File: WP3_D5_Innovative integration system concepts_final.doc

NEGST – NEW GENERATION OF SOLAR THERMAL SYSTEMS is a project financed by the European Commission DGTREN within FP6

1 SUMMARY

This report contains examples of efficient methods for integration of solar thermal products into the energy systems of new and existing buildings.

There is a number of typical conventional space heating and domestic hot water systems for both single-family and multi-family buildings in Europe. For each of these conventional systems, examples of solar thermal systems are described that match the requirements of the respective conventional system and can easily be integrated. The examples show which style of solar thermal system allows simple integration into a given conventional heating system. It does not necessarily show the ‘perfect solution’. An important aspect of integration of solar thermal systems in conventional heating appliances is to assure that the integration guarantees good conditions for thermal performance of solar systems – it gives priority to the sun. These examples are chosen taking this rule into consideration.

Some of these examples are already on the market in one or more European countries. Some are just ideas that have not been implemented yet, but are promising new approaches.

The first part of the report deals with systems for single-family houses. It is shown how solar thermal can be integrated into conventional combined heating systems with or without separate domestic hot water store or in systems with completely separate heating systems for space heating and domestic hot water.

The second part of the report shows conventional systems for multi-family houses and how solar thermal can be integrated into 2-pipe and 4-pipe networks as well as conventional systems with separate domestic hot water stores in each apartment.

WP3.D5Recommendations for Concepts for Easy

Installation and Integration in ConventionalHeating Appliances

Dissemination level: Public Charlotta Isaksson, Dagmar Jähnig, AEE INTEC

Reviewer: M.J. Carvalho, INETIDecember 2005

CONTENTS

SYSTEMS FOR SINGLE-FAMILY HOUSES

Combined heating systems with and without DHW store

DHW systems

SYSTEMS FOR MULTI-FAMILY HOUSES

Centralized solar thermal systems

Decentralized solar thermal systems

AKNOWLEDGEMENTS

The following people have contributed to this report:

AEE INTEC: Dagmar Jähnig, Charlotta Isaksson

CSTB: Bouzid Khebchache

INETI: Maria João Carvalho

ITW: Harald Drück, Elke Streicher

Paradigma: Stefan Abrecht

SERC: Chris Bales

University of Oslo: Michaela Meir, Rohn Rekstad

Concepts for Integration in Conventional Heating Appliances – December 2005 page 2 of 21


2 Table of Contents 1 SUMMARY 1 2 Table of Contents 2 3 Introduction 3 4 Single-Family Houses 3

4.1 Conventional Combined Heating System with DHW Store 3 4.1.1 Two Heat Exchangers in DHW Store 3 4.1.2 Solar Thermal System with High Temperature Collector Loop in Parallel to a

Conventional Boiler 4 4.2 Conventional Combined Heating System without Separate DHW Store 6

4.2.1 Compact Solar Combisystem 6 4.2.2 Combisystems with Water as Heat Transfer Medium Avoiding Heat Exchangers 8 4.2.3 Solar Thermal System Attached to Conventional Combined Boiler with Built-in

DHW Store 10 4.3 Separate Systems for Domestic Hot Water and Space Heating 11

4.3.1 Solar Thermal System with Storage Tank for Preheating of Domestic Hot Water 11 4.3.2 Solar Thermal System with External Heat Exchanger for Retrofitting of

Conventional Electrically Heated DHW Stores 12 4.4 Solar Thermal System for Weekend Houses 13 4.5 System Controller 13

5 Multi-Family Houses 14 5.1 Conventional System with 2-Pipe Heat Distribution Network 14

5.1.1 2-Pipe Networks with Apartment Heat Transfer Units 15 5.1.2 2-Pipe Networks with DHW Store in Each Apartment 16

5.2 Conventional System with 4-Pipe Heat-Distribution Network 17 5.3 Conventional System with Separate DHW System for Each Apartment 18

5.3.1 Decentralized Solar Thermal System for Domestic Hot Water Preparation in Each Apartment 18

5.3.2 Central Solar Thermal System for Decentralized DHW Stores 19 5.4 Energy Metering for Heat Distribution Networks 20



3 Introduction This report contains examples of efficient methods for integration of solar thermal products into the energy systems of new and existing buildings.

There is a number of typical conventional space heating and domestic hot water systems for both single-family and multi-family buildings in Europe. For each of these conventional systems, examples of solar thermal systems are described that match the requirements of the respective conventional system and can easily be integrated. The examples show which style of solar thermal system allows simple integration into a given conventional heating system. It does not necessarily show the ‘perfect solution’. An important aspect of integration of solar thermal systems in conventional heating appliances is to assure that the integration guaranties good conditions for thermal performance of solar systems – it gives priority to the sun. These examples are chosen taking this rule into consideration.

Some of these examples are already on the market in one or more European countries. Some are just ideas that have not been implemented yet, but are promising new approaches.

4 Single-Family Houses Three conventional heating systems for single-family houses and good examples for integration of a solar thermal system into these conventional systems are described below.

4.1 Conventional Combined Heating System with DHW Store

Fig. 1: Conventional space heating system with domestic hot water store

The system shown in Fig. 1 consists of a domestic hot water store that is heated with a conventional boiler. The boiler heats both the domestic hot water store and directly into the space heating loop.

4.1.1 Two Heat Exchangers in DHW Store In many cases, it is possible to install two heat exchangers in the domestic hot water store, but only the lower one is used to heat the store with the boiler. To integrate a solar thermal system, the boiler can be connected to the upper heat exchanger so that the lower heat exchanger can be connected to the collector loop. This is shown in Fig. 2.

Fig. 2: Conventional space heating system with domestic hot water store



4.1.2 Solar Thermal System with High Temperature Collector Loop in Parallel to a Conventional Boiler

In this case, the collector loop of the system is directly connected to the conventional system like a second boiler see Fig. 3. The solar collector must deliver high flow temperature in order to compete with the boiler, which delivers the temperature needed for domestic hot water.

Fig. 3: Conventional space heating system with domestic hot water store and integrated solar

collectors

The ‘AquaSystem’ concept by the German company Paradigma uses a standard domestic hot water store with one heat exchanger and connects a water-filled evacuated tube collector to the existing piping between hot water store and auxiliary boiler (see Fig. 4).

The piping of a vacuum tube collector with CPC reflector is directly connected by trap elbows to the conventional system like a second boiler. The collector is operated on the same or higher temperature level as provided by the boiler. It is the same water which runs through the collector and the boiler. An innovative frost protection algorithm with minimal energy consumption prevents the collector loop from freezing. The basic idea of this frost protection is that vacuum tube collectors do not require frost protection in the same extent as the piping. The piping is protected by briefly turning on the collector loop pump if frost protection is needed. Almost every heat store with a single heat exchanger can be retrofitted with this system. Furthermore the advantage of using water without antifreeze is the reduced risk of clogging the collector piping by sediments that are separated from the glycol due to the high temperatures that occur during stagnation.

The dimensioning of the collector area of the system is 1 m² per person + 1 m² for the heat losses of the piping. The maximum allowable collector area is 1 m²/40 l storage volume.



Fig. 4: AquaSystem with vertical conventional DHW store (source: Paradigma, Germany)

Another option is to include the possibility of direct solar space heating (see Fig. 5).

The system is connected and operated like the DHW-AquaSystem. An additional pipe connects the flow of the solar circuit with the space heating circuit. The solar heat can be either transported into the DHW store or directly into the flow or return line (depending on the heat capacity of the boiler) of the space heating loop. The distribution of the solar heat is done by a three-way-valve in the flow line of the solar circuit. Different strategies of distributing the heat are available. The dimensioning of the collector area of the system is 1.5 m² per person + 1 m² for the heat losses of the piping. The maximum allowable collector area is 1 m²/40 l storage volume.

Fig. 5: DHW-AquaSystem with additional direct solar space heating (source: Paradigma,

Germany)



4.2 Conventional Combined Heating System without Separate DHW Store Systems with a compact conventional boiler that have a small built-in domestic hot water container and provide both domestic hot water and space heating for a single-family house are in this category.

Fig. 6: Conventional system without domestic hot water store

4.2.1 Compact Solar Combisystem Systems without a domestic hot water store can easily be replaced by a compact pre-fabricated solar combisystem. These systems contain all necessary components for the whole heating system and are fully industrially manufactured and packaged. These systems are typically storage tanks with an integrated fossil or pellets burner. The number of hydraulic connections that have to be made is very low: 2 x collector loop, 2 x space heating loop, 2 x domestic hot water.

Fig. 7: Compact Solar Combisystem

Examples for this type of system are shown in Fig. 8 through Fig. 12. These systems have a gas, fuel oil or pellet burner integrated into the store (Fig. 8, 9 and 10) or cabinet (Fig. 11 and 12).



Fig. 8: Compact solar combisystem with integrated pellet burner by the company

Solarfocus, Austria

Fig. 9: Compact solar combisystem with integrated gas or fuel oil burner by the

company SOLVIS, Germany

Fig. 10: Compact solar combisystem with integrated gas burner for direct solar floor

heating by the company CLIPSOL, France

The following two figures show combisystem designs that consist of one or two cabinets, often of standard dimension 60 x 60 cm, and require a minimum of external connections. These systems do not have an auxiliary heater integrated into the store but it is included into the cabinet. They are designed so that they can be placed in the living space and not necessarily in the basement of a house.



Fig. 11: Compact solar combisystem including a gas or pellet burner built into two 60 x 60 cm cabinets, system being developed by DTU,

SERC and MetroTerm in Denmark and Sweden

Fig. 12: Small compact solar combisystem in one single cabinet with solar store below a boiler/store with gas burner above, from the

company Daalderop, The Netherlands

4.2.2 Combisystems with Water as Heat Transfer Medium Avoiding Heat Exchangers There are systems that are slightly less compact compared to the systems shown in paragraph 4.2.1. However, they avoid heat exchangers in the solar loop by using water as heat transfer medium.

4.2.2.1 CPC Vacuum-Tube Collectors (Pressurized Single-Loop Systems)

These systems by the German company Paradigma are operated in the same way as DHW AquaSystems. Heating water flows through the collector and is heated as much as possible (60°C - 90°C) in a single circulation. The solar loop is connected directly to the combistore without a heat exchanger. The circulation pump takes out the cold water in intervals from the bottom store and feeds directly the upper part of store, so that a good stratification is built up. In the upper part of the store there is a small built-in DHW tank (TITAN) or a heat exchanger to prepare the DHW instantly (OPTIMA). A separate DHW store is therefore not necessary. There are two ways of connecting the space heating system to the combistore. The first alternative is shown in Fig. 13, which shows that the flow of the combistore feeds into the return flow of the boiler and then the heating circuit (= increasing of return temperature). The second possibility (shown in Fig. 14) is, that the boiler also feeds the combistore for space heating and the space heating circuit takes out the necessary heat directly from the combistore (= buffer principle). The dimensioning of the collector area of the system is 2 m² per person + 1 m² for the heat losses of the piping. The dimensioning of the volume of the combistore is about 60 - 80 l/m² collector area.



Fig. 13: AquaSystem with combistore TITAN operating connected to increase the space heating return temperature (source: Paradigma, Germany)

Fig. 14: AquaSystem with combistore Optima operating with the buffer principle (source: Paradigma, Germany)



4.2.2.2 Non-pressurized Drain-Back System

A simple and low-cost solar heating system is a design where the heat buffer store, the solar collector- and the floor heating loop are not pressurized and connected without intermediate heat exchangers. The system contains water as heat transfer medium. In the present example, the solar collectors are drain-back collectors and the heat storage acts also as drain-back reservoir.

Fig. 15: Drain-back collector system with water as heat transfer medium and without

intermediate heat exchangers by Solarnor, Norway

4.2.3 Solar Thermal System Attached to Conventional Combined Boiler with Built-in DHW Store

Another system concept by the German company Paradigma allows attaching a solar thermal system to a conventional combined gas or oil boiler with integrated small domestic hot water store.



Fig. 16: AquaSystem with horizontal conventional DHW store (source: Paradigma, Germany)

Again, it is a system using water as heat transfer medium in the evacuated tube collectors similar to the other AquaSystem concepts described above.

4.3 Separate Systems for Domestic Hot Water and Space Heating In many parts of Europe as well as in North America, DHW production and space heating is not a combined system but separate units. The space heating can be by point sources, air or other heating systems.

Fig. 17: Separate systems for domestic hot water and space heating

The system shown in Fig. 17 consists of a domestic hot water store and a separate space heating system, which can be point sources, air or other heating systems. The heat for the store is often supplied by electricity via a heating element.

4.3.1 Solar Thermal System with Storage Tank for Preheating of Domestic Hot Water In this case, a solar thermal system is used for preheating of domestic hot water, using the existing DHW store as auxiliary system, as can be seen in Fig. 18. A standard electrically heated DHW store is used and the solar thermal system can be attached simply at the inlet of the conventional store.



Fig. 18: Integration of solar thermal system (preheat) with an existing electrically

heated DHW store

4.3.2 Solar Thermal System with External Heat Exchanger for Retrofitting of Conventional Electrically Heated DHW Stores

For electrically heated stores, there are only two connections, one for mains inlet and one for hot water outlet. A solar thermal system can be connected to these two ports and supplies heat through them, normally via an external heat exchanger as shown in Fig. 19. The flow on the store side is normally natural convection. This type of system is easy to connect to existing systems.

A possible solution is marketed by the Canadian company Enerworks. For charging of the store, the flow valve is open and water can enter the heat exchanger by natural convection through the bottom connection and the hot water enters the store at the top (see Fig. 19 bottom). For DHW discharge and higher flow, the flow valve is closed, the water back flushes the heat exchanger and enters the store at the bottom (see Fig. 19 top).

Flowvalve

Flowvalve

Fig. 19: Conventional electrically heated DHW store with solar collector connected to it via heat transfer unit consisting of an external heat exchanger with special back flushing configuration for

anti-fouling, by the company Enerworks, Canada.



4.4 Solar Thermal System for Weekend Houses In weekend houses in southern climates, it may be interesting to have the possibility to use the solar thermal system for hot water preparation on weekend days and space heating on week days. During the week the space heating guarantees a low level comfort temperature in the house and avoids humidity. A schematic of this system concept is shown in Fig. 20.

Fig. 20: Weekend house system – alternately used for space heating (week days) and domestic

hot water heating (weekend)

4.5 System Controller A controller that can control the entire system (collector loop, domestic hot water preparation, space heating loop(s), circulation loop, auxiliary heating), can be helpful to ensure proper functioning of the system. Non-matching control strategies of separate controllers can be avoided.

An example from Austria with 16 inputs and 11 outputs is shown in Fig. 21. This controller also includes the possibility to measure energy, e.g. solar yield.

Fig. 21: System controller with 16 inputs and 11 outputs by the company Technische Alternative,

Austria

Another example from Norway additionally includes energy metering of the solar heat production, the auxiliary energy supply and the delivery to the space heating system (Fig. 22). An easy read-out on the display motivates energy-conscious consumption behaviour and is in line with the new EU directive on the performance of buildings /EU02/. The energy monitoring can be realized at low costs without adding new sensors or components to the control system.



Fig. 22: Controller for the entire solar heating system with energy metering by the company

Solarnor, Norway

5 Multi-Family Houses Heating systems in multi-family houses vary significantly depending on the specific project. There are centralized and decentralized systems. Heat sources and heat distribution systems can be different. Some systems are more and some are less suitable for integration of solar thermal energy.

The following sections show some concepts and ideas where integration of solar thermal can be done with moderate effort.

5.1 Conventional System with 2-Pipe Heat Distribution Network A quite common heating system in multi-family houses uses a central conventional boiler or district heating to supply both domestic hot water and space heating. A 2-pipe heat distribution network is used to deliver the heat to the apartments.

There are two varieties of this system. For relatively compact multi-family buildings with short distances between the different users, so-called apartment heat transfer units are used to control the space heating loop flow and return temperature and to supply heat for domestic hot water using a heat exchanger. This is shown in Fig. 23.

Fig. 23: Conventional system with 2-pipe network

For longer distances between users such as in terraced houses, small domestic hot water stores are installed in each apartment. These stores are charged in specified time windows once or twice a day. This way, the heat distribution network has to be operated at domestic hot water temperature (55-60°C) only during these time windows. For the rest of the time, the temperature in the network can be lowered to the temperature necessary for space heating. Thereby, heat losses from the network are reduced.



5.1.1 2-Pipe Networks with Apartment Heat Transfer Units The heat distribution system can stay exactly the same as in the conventional system if apartment heat transfer units are used. The apartment heat transfer units are an essential part of the system because they ensure that the return temperatures from each apartment are as low as possible. The space requirements for the heat transfer unit are very small. They can even be flush-mounted in the wall (see Fig. 24).

Fig. 24: Flush-mounting of an apartment heat transfer unit (left) and example apartment heat transfer unit by the company Redan, Denmark

The idea of the apartment units originated in Scandinavia and they are already equipped with practically all the components required to ensure an efficient and unproblematic operation of the domestic heat supply. Moreover, they are not only compact and industrially manufactured to the highest quality but also feature components that do not require an external power supply. Although decentralized apartment units were originally used in the field of district heating, there are now several suppliers in Europe who supply units specially developed for use in multi-storey residential buildings /Fin04/.

Properly equipped apartment units contain all the components required to provide decentralized heating of domestic hot water, to provide a hydraulic equalization of the space heating circuit, and for long-term operation and maintenance. Fig. 25 shows a block diagram of the two-dimensional functional layout of the components.



Fig. 25: Block diagram of the functional layout of the components in an apartment heat transfer

unit and typical operating temperatures.

The system needs an additional buffer store where both the collectors and the conventional boiler deliver heat into. The 2-pipe network is fed from the top of the buffer store. The low return temperature from the network go into the bottom of the store and ensures low return temperatures to the collectors and therefore high solar yields (see Fig. 26).

Fig. 26: Central solar thermal system for buildings with 2-pipe network

5.1.2 2-Pipe Networks with DHW Store in Each Apartment

Fig. 27 shows the block diagram of a solar-supported heat supply system featuring heat distribution via a two-pipe network plus decentralized heating of the domestic hot water in daily storage tanks.



Fig. 27: Solar-supported concept for heat distribution: two-pipe networks connected with the

decentralised domestic hot water storage tank

As with the two-pipe network for apartment heat transfer units, the heat storage unit is the central point for all heat flows and acts as a hydraulic switch. 5.2 Conventional System with 4-Pipe Heat-Distribution Network Another common heating system in multi-family houses uses a central conventional boiler or district heating to supply both domestic hot water and space heating. A 4-pipe heat distribution network is used to deliver the heat to the apartments (see Fig. 28).

The first pair of pipes is operated at about 55 - 60°C and delivers domestic hot water to each apartment. The second pair of pipes is used for space heating and is operated at much lower temperatures.

Fig. 28: Conventional heating system for buildings with 4-pipe network

4-pipe networks have higher heat losses compared to 2-pipe networks. Therefore, 2-pipe networks are preferable for new houses. However, existing 4-pipe networks can be retrofitted with a solar thermal system using a concept similar to the one for 2-pipe networks. Here, the additional heat store can be used for domestic hot water only or as a combistore. In the first option, the connection of the conventional boiler to the space heating network stays the same. In addition the boiler is connected to the store that is also heated by the solar thermal system. There are different possibilities to connect the heat distribution network to the store depending on the chosen store type (tank-in-tank, DHW store with heat exchanger for space heating etc.). Fig. 29 shows only a schematic drawing of a solar-assisted 4-pipe network.



Fig. 29: Central solar thermal system for buildings with 4-pipe network

5.3 Conventional System with Separate DHW System for Each Apartment Another typical scenario for multi-family houses is that the domestic hot water is provided by decentralized domestic hot water stores in each apartment. The auxiliary energy of the decentralized hot water stores is often electricity (see Fig. 30).

Fig. 30: Conventional system with separate DHW system for each apartment

The space heating system can be a central boiler or district heating system or decentralized boilers in each apartment. A solar thermal system would in both cases be integrated into the individual domestic hot water boilers and not supply any heat for space heating.

5.3.1 Decentralized Solar Thermal System for Domestic Hot Water Preparation in Each Apartment

A possible system configuration for integration of solar thermal in decentralized domestic hot water stores is to add a heat exchanger to each domestic hot water store and to connect it to a part of a collector field that is mounted in the façade of the building. This means that pipe connections from the collector into the apartment are very short. A simple controller could allow the electrical heating element to heat the store only after sunset, if there was not enough solar radiation to bring the store to the desired temperature. The system schematic is shown in Fig. 31, a sketch of the collector and storage tank configuration in Fig. 32. The solar thermal collectors can be installed integrated into the façade itself or, for example, into the balustrade of south-facing balconies.



Fig. 31: Decentralized solar thermal system for domestic hot water preparation in each

apartment

Fig. 32: Sketch of the collector and storage tank configuration

5.3.2 Central Solar Thermal System for Decentralized DHW Stores If integration in the façade is not considered or possible, the following solution can be adopted, specially for low latitudes (southern Europe) for which vertical placement of the collectors corresponds to a strong penalty. In this case, it is better to install the collectors in the roof with a tilt equal to the latitude.

The system consists of a centralized solar thermal system for decentralized domestic hot water stores, each with a heat exchanger. The heat exchangers are connected to a collector field. The hydraulic connections from the collector field to the heat exchangers allow to distribute heat to all domestic hot water tanks in almost equal parts because they are all connected in parallel. The control is made comparing the temperature in the collector field to the return temperature from the heat exchangers in the storage tanks. Fig. 33 shows schematically how this is done.

Also in this case, a simple controller could allow the electric heating element to heat the store only after sunset, if there was not enough solar radiation to bring the store to the desired temperature.



Fig. 33: Centralized solar thermal system for domestic hot water preparation in each apartment

5.4 Energy Metering for Heat Distribution Networks In heat distribution networks with a central heat store for the solar thermal system and the auxiliary energy supply, it is important to have individual energy metering for the consumers in each apartment. The apartment owners are charged according to their energy consumption. Hence, energy-conscious behaviour is motivated. Especially for houses with a low-temperature heat emission system, the energy metering (space heating) is not trivial. One solution is that one temperature controller in each apartment regulates the energy transfer from one common heating central to each apartment. The controllers regulate the energy supply, the heat carrier's mass flow, through automatic valves. A commonly used technique is to modulate the heat carriers mass flow or to mix the hot heat carrier from the heat source with the heat carrier returning from the heat distribution system by means of a shunt valve.

Here, the automatic valves are modulated on an on/off basis. The heat carrier is supplied in terms of energy pulses. The length of these pulses (duty cycle) is dependent on the actual heat demand. In heating systems with a large thermal mass (floor-/wall heating), intermittent heat supply does not create discomfort. Further, pulsed energy supply offers an easy principle for energy metering based on the duty cycle information, instead of monitoring the temperature difference and the volume flow of the heat carrier. No additional sensors and components have to be installed for the present metering strategy /REK02/.

Additionally, the individual controllers can be equipped with a two-way communication module (LONTM technology) that can be read out and reprogrammed through a network independently of the users. This procedure is of advantage for the energy supplier who needs to charge the apartment owners according to their consumption. The controllers monitor the space heating and the DHW consumption.

Fig. 34: Controller with energy metering function for low temperature heating systems in multi-

family houses by the company Solarnor, Norway



References

/Fin04/ Fink C., Riva R. (2004): Solar-supported heating networks in multi-storey residential buildings - A planning handbook with a holistic approach Published in German by Arbeitsgemeinschaft ERNEUERBARE ENERGIE GmbH, Gleisdorf, Austria. An English version is available electronically from AEE INTEC, Gleisdorf, Austria

/EU02/ EU-DIRECTIVE (2002), Directive 2002/91/ec of the European Parliament and of the council of 16 December 2002 on the energy performance of buildings. Official Journal of the European Communities, Brussels, January 4, 2003, L1/65 [online, 10.06.2005]: http://europa.eu.int/scadplus/leg/en/lvb/l27042.htm

/REK02/

Rekstad J., Meir M., Kristoffersen A. R. (2003): Control and energy consumption monitoring in low temperature heating systems. Energy and Buildings 35, 281-291

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WP3.D5 Recommendations for Concepts for Easy Installation and