Practical Experiences with Zonal Control and Remote Access: Honeywell Evohome Case Study

Zonal control is the most modern approach to heating regulation in houses and apartments. It ensures the highest comfort and is also one of the ways to reduce heating costs.

Zonal heating control means controlling the room temperature of individual rooms (zones) of a family house or apartment according to a specified weekly schedule. The weekly schedule is created for each room separately. The program is set to best match the usual usage pattern of the individual rooms. This achieves living comfort and energy savings. Remote access to zonal control is usually done via a mobile app or web interface.

Remote control can have several levels. The basic level provides an overview of the measured temperatures in the rooms and allows changing the desired temperature of each room. Extended levels of remote access can then be used to obtain data and information about the heating system's behaviour. It is possible to display not only the current state and parameters of the system.

IMPACT OF HEATING SYSTEM MODIFICATIONS ON ENERGY CONSUMPTION

The monitored object is a basement row apartment building, built in 1937, and no structural modifications (such as insulation) were made before data collection began. The building contains 5 small separate apartment units on three above-ground floors. In total, there are 13 living rooms where zonal control Honeywell Home - Evohome is now newly used.

The entire building is heated by a gas boiler, controlled by an equithermal regulator with a weekly schedule. Individual rooms are heated by cast iron radiators equipped with thermostatic valves.

Monitoring Energy Consumption for Heating the Object

Energy consumption was measured over 24 years. During this period, three modifications affecting the heating system were made. The following graph shows the year-on-year energy consumption. The vertical axis shows the net energy consumption. The graph also marks events when such investments in the object were made that affected energy consumption.

State 0 is the initial situation after the central heating was put into operation in 1995. The heating source was a 35kW atmospheric gas boiler equipped with equithermal regulation with a time program, without correction for indoor temperature. Cast iron heating bodies and valves with manual thermostatic heads were installed in the living rooms.

Investment A is the replacement of sash windows with plastic ones throughout the building. The investment amounted to 480,000 CZK.

State 1 illustrates the operation of the existing central heating, consumption decreased due to window replacement. The average annual consumption during these three years is 13% lower.

Investment B illustrates the impact of the installation and commissioning of the wireless zonal system Evohome in all living rooms. The value of this investment in heating regulation was 72,000 CZK.

State 2 represents the operation of zonal control. The thermostatic valves of the heating bodies are now controlled by wireless HR92EE heads or MT4 thermal actuators. Wireless temperature sensors/controllers T87 Round are used to obtain the reference temperature of each room. Zonal control has no connection to boiler control; equithermal regulation with a weekly schedule is maintained. All elements of zonal control communicate with the Evohome control unit, which stores individual weekly schedules (different for each room). The schedules are adapted to the tenants' lifestyle, and each can set the desired temperature to a maximum of 23°C. The Evohome control unit contains a Wi-Fi module and is connected via a home router to a remote server. The server receives requests for mode changes or temperature settings (e.g., from a mobile app) and sends them to the control unit. The server also continuously collects various data about the system's behaviour and can provide it upon request. The average annual consumption decrease compared to state 1 is 19%, and compared to the initial state 0, it is 30%.

Investment C means replacing the heat source. The atmospheric boiler was replaced with a condensing boiler. The investment also includes a new flue liner. Since investments A and B allowed reducing the demand on the central heat source's output, a boiler with a lower output of 30kW could be used. A new equithermal regulation was supplied along with the boiler. The cost of acquiring the boiler and installation work amounted to 88,000 CZK.

State 3 is the current operation of zonal control and the new condensing boiler. The boiler is again controlled purely equithermally. It has no connection to the zonal system. The reduced boiler output further contributed to the consumption reduction, as the boiler operates with higher efficiency during the transitional period (autumn and spring). Investment C thus brings additional energy savings, compared to the previous state 2 it is 27%, and compared to state 0 it is already 49%.

The comparison shows that the current heating system consumption is approximately half compared to the initial period before investments (state 0).

The table shows the contribution of individual investments to the achieved savings. While the highest, relatively significant structural investment in window replacement brought the smallest energy savings. Investments in technological equipment, which were significantly lower, proved to be far more effective.

ANALYSIS OF THE IMPACT OF ZONAL CONTROL ON ENERGY SAVINGS

Zonal control generated a 19% saving in our case study. The effect can be divided into three basic functions:

• Room temperature control in individual rooms
• Remote access - viewing and control
• Scheduled program for setting desired temperatures in individual rooms

Room Temperature Control

Room temperature control in individual rooms was originally (i.e., state 0) implemented through ordinary manual thermostatic heads. Manual thermostatic heads could maintain the set temperature in rooms as accurately as zonal control elements.

Remote Access

Remote access is a modern feature. However, people with a regular weekly routine use it relatively rarely. A person who acquires a zonal system closely monitors how everything works for a month after installation. After a month, however, they let the heating regulation live its own life and do not use remote access very often. In the long term and with regular use, remote access has little impact.

Scheduled Program

The scheduled program can prevent losses caused by human negligence. Residents often set a high comfort temperature and then leave the house. Because Evohome automatically switches to setback temperatures during absence. Evohome can also maintain economically viable temperature settings. Residents of the house only increase the desired temperature in their room when they start feeling cold. The scheduled program also brings comfort. It is no longer necessary to wake up in cold rooms in the morning.

OPERATION OF ZONAL CONTROL

The installation of zonal control alone cannot ensure the expected savings. It is also necessary to know how to use it correctly and thoughtfully. If someone invests in it to reduce heating bills and then permanently sets the desired temperature to 24°C in all rooms, they will be disappointed. When using zonal control, it is also advisable to ensure that individual rooms (zones) are as spatially closed as possible. If rooms are separated by doors, the doors should not remain open all the time. Then, although one room may be set to a comfort temperature and another to a setback temperature, both will be heated to the comfort temperature.