INSERTION OF BOILERS IN HOME AUTOMATION SYSTEMS D. Scaradozzi*, G. Conte*, V. Aisa** *Department of Electronics and Automation Università Politecnica delle Marche Via Brecce Bianche – 60131 Ancona – Italy Tel.: +39(71)2204844/4314 – Fax: +39(71)2204834/5 E-mails:
[email protected],
[email protected] **Wr@p s.p.a. Via Serraloggia 78/a – 60044 Fabriano – Italy Tel.: +39(732)6362634 E-mail:
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Keywords: Home Automation, Domotics, Boiler, Energy Consumption Introduction Appliances of different kind can be grouped in modern home automation systems in order to optimize energy consumption and to increase user satisfaction. Some of these appliances (like washing machines and dishwashers) use electricity for producing hot water, which could more economically be obtained by a boiler, either employing gas or using in more efficient way electricity. On the other hand, boilers employ electricity for circulating hot water in the house heating circuit, for evacuating combustion residues, for ignition and for other tasks. For all these reasons, the insertion of a boiler in a home automation system turns out to be an interesting topic to investigate. In this paper, we consider a home automation system consisting of a communication network that connects several appliances and a special device for measuring the actual energy consumption. The measuring device provides information to the connected appliances, which may exchange data on the network for managing energy consumption, so to avoid peaks that exceed the maximum availability or to take into account variations in the energy price during the day. In addition, the possible presence of a residential gateway assures external communication that can be used for monitoring and security (see [4],[5] and [6]). The insertion of the boiler in this framework is actuated by means of a Wr@p Enabled Smart Adapter (WESA), which monitors the energy consumption of the boiler and makes this information available on the communication network to all connected appliances. Use of the WESA enables the boiler to become an element of the home automation system independently from its built-in characteristics. By characterizing the boiler behaviour in terms of actual energy consumption, we develop a suitable procedure for enabling the home automation system to employ the boiler in producing hot water for other appliances. This is done in accordance with the requirements of the home heating system and assuring satisfactory hot water availability for domestic use. As an additional feature, the possibility to communicate through the residential gateway allows to monitor from an outside location the behavior of the boiler, so to increase operational safety and to facilitate maintenance.
Description of the home automation system Home automation systems consist of a number of appliances which can exchange information on a communication network of some kind. The system may include a central control unit and appliances may be endowed with individual control systems, so to enable the overall system to manage energy consumption or to perform specific tasks which require coordination and/or cooperation. To fix the ideas, we can make reference to the Ariston-Digital structure described in [1],[4] and [9]. In the considered home automation system the appliances are connected to the power line through a special device called Wr@p Enabled Smart Adapter (WESA) (see [8]), whose basic function is that of allowing communication using the power line as carrier and employing a suitable protocol. The WESA is capable to measure the energy consumption of the
connected appliance and, provided it has additional information about the appliance’s behaviour, it can monitor its functions and detect its status. Appliances endowed with a suitable interface can also be controlled by WESA. In this structure, the WESA nodes concentrate (part of ) the intelligence of the overall system and they, together with the central control unit, if it is present, implement the software procedures which allow it to work as a (partially) distributed control system (see [2] and [3]. Concerning energy consumption, the main task of an home automation system is that of avoiding peaks that exceed either fixed or time depending thresholds. To facilitate this task, the home power system is assumed to include a power meter, which informs the home automation system about current consumption and energy availability (see [6]). Clearly, in case of conflict, the system has to assign priority and to distribute the available energy accordingly. Remarking that appliances like washing machine and dishwasher employ large amount of electricity for producing hot water, it is clear that potentialities and performances of the overall system could be increased by making directly available hot water as a new resource. Hot water can in fact be produced in a more efficient and economic way by means, for instance, of a gas boiler or of a central heating system. We consider here the first alternative, since individual gas boilers are present in a large number of modern houses. On the other hand, the use of a new resources, which is of course limited, may generates conflicts among the appliances which are given the possibility to employ it and, possibly, with other users that originally were not considered and are not part of home automation system. In order to govern this situation, a first thing we can do is to enlarge the home automation system by connecting to it the boiler and, possibly, (some of ) the hot water users. In the case of the boiler, this is easily done by exploiting the fact that gas boilers employ electricity in a number of tasks (like circulating hot water, evacuating combustion residues and other minor tasks). By using a WESA node, the boiler is included within the home automation system without requiring further interventions of any kind (see [8]). At the present stage, it is not reasonable to assume that the WESA node can control the boiler, as it may be with appliances of other kind, since the operation of gas boilers is subject to strict safety norms. However, the WESA can make available to the system the information about the behaviour and the status of the boiler it can deduce from electric energy consumption. Among the hot water users that originally were not considered in the home automation system, we have the house heating circuit and a generic human user. Although it could be possible to have evidence of their behaviour by means of specific sensors, this would be in general very expensive and it could require heavy intervention on the house structure. Then, we are motivated to choose a different solution, that consists in giving the home automation system the possibility to interact with external agents, like the two users we are considering, on the basis of the information which is internally available. This amounts to assume that the home automation system can neither directly observe the requests of the house heating circuit and of the generic human user nor it can control them, but it has to rely on the information about the boiler behaviour the WESA can supply. Moreover, we assume that the home automation system may prevent any other agent (e.g. washing machine or dishwasher) from employing the hot water produced by the boiler and we consider only the situation in which the boiler is powered on. A scenario of the kind considered above is represented in the scheme of Figure 1.
Fig. 1. Home automation system scheme.
The scenario includes a dishwasher DW and a washing machine WM, both connect to the water net. In this scheme the water net distributes cold and/or warm water, the second one being produced by a gas boiler GB. The house heating circuit
and a generic human user are indicated respectively by USER and HC. The appliances and the boiler are connected to the power line through WESA nodes, indicated by N. A power meter PM, coupled with a power limiter PL, separates the house electric circuit from the external source. An additional element of the system is represented by a residential gateway, which allows communication between the home automation system and the rest of the world.
Hot water management in the home automation system Energy consumption, in an home automation system of the kind we have described, can be managed by suitable power levelling algorithms, as for instance that developed by WRA@P and described in [7] and [9]. Essentially, each appliance is given a priority level and energy is distributed accordingly. The priority levels are not fixed, but they vary depending on the time spent in waiting for the resource become available and on the machine status. In this way, using an intelligent control approach, the system becomes able to solve conflicts generated by concurrent needs of the various appliances and to govern the use of limited resources. When the hot water resource is present, its use can in principle be ruled by a priority levels policy similar to that employed for managing electric energy. This method may solves conflicts between the various appliances, but it remains the problem of interacting in a satisfactory way with the external users. To this aim, it is necessary to give the home automation system evidence of the activity of such users. The method we propose consists in monitoring, through the WESA, the electric consumption of the gas boiler, that is mainly due to the activation of two internal electric devices: • a water pump, used both for circulating hot water in the house heating circuit and in the internal heat exchanger, • a fan, used for assisting combustion by discharging to and drawing the combustion air from outside of the room. Energy consumption of the water pump, when it is active, is generally constant, while energy consumption of the fan depends on the quantity of heat required for responding to the user demand. From the point of view of the boiler, there are in facts two different users: the house heating circuit and the domestic water net. Remark that the boiler is designed in such a way to give absolute priority, in case of concurrent demands, to the water net. Analysing gas boilers of different brands and similar characteristics, it has been found that, for what concerns electric energy consumption, three different modes are clearly detectable in the typical behaviour. Figure 2 below show the energy consumption of a 23 kW instantaneous, wallhung, room sealed, fan assisted gas boiler over a 30 min period.
Fig. 2. Boiler power consumption .
The coloured areas in the above diagram have the following meaning: • • • •
green (A) blue (B) yellow (C) orange (D)
= = = =
pump and fan are inactive; pump is active, fan is inactive ; pump is active, fan is active and exerting a moderate effort; pump is active, fan is active and exerting a strong effort.
The different modality in the fan behaviour depend on the quantity of heat required for responding to the user’s demand. The boiler/house heating circuit works actually as a closed loop control system and the fan is called only to actuate a moderate control effort to satisfy the house heating circuit demand. The boiler/water net system, instead, is designed to produce the maximum effort in response to any demand, so to satisfy it in the shortest possible time. We can therefore deduce that, if no appliance is demanding hot water, each one of the four areas described above characterizes a different situation as illustrated below: • • • •
green (A) blue (B) yellow (C) orange (D)
= no external user is demanding hot water, the house eating circuit is disabled; = no external user is demanding hot water, both external users are enabled; = the house eating circuit is demanding hot water; = the generic human user is demanding hot water.
The home automation system knows whether any one of the connected appliances is currently demanding hot water and can get information about the external users activity by means of the boiler’s WESA node and the above correspondence table. Then, it can implement a policy that, for instance, assures absolute priority to the generic human user with respect to any appliance and that, exploiting the fact that the boiler gives priority to the domestic water net with respect to the house heating circuit, regulates conflicts between all other users, namely appliances and the house heating circuit, by suitable rules.
Conclusion Motivated by energy saving reasons, a feasible way for inserting a boiler in a modern home automation system has been developed and described. The analysis of the boiler electric energy consumption is used to obtain information about the external users activity, so to support the home automation system in the decision making process. The main feature of our approach consists in giving the home automation system the possibility to manage the hot water resource resolving the conflicts due to concurrent demands without interfering with the boiler normal operation and the human user’s habits.
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