Controlling hot water supply in a vented system

How does a vented hot water system work?

Refer to the diagram below

A vented hot water system is one fed from a cold water storage tank (A) – typically in the loft of the house.

Water gets into this tank directly from water main with a pipe that rises vertically into the loft of the house. This is often referred to as a “rising main” (B). Cold water from this tank fills a cylinder (C) which acts as another tank. This cylinder is insulated.

A hollow internal copper coil or heat exchanger is built inside the cylinder (D). Water inside the coil and water inside the cylinder never mix. Water in the internal coil is heated using a boiler (E) and

moved around with a pump (F). So the hot water from the boiler will circulate inside the

coil which is inside the cylinder. In this way, the water in the cylinder is heated up.

The hot water cylinder has a thermostat (G) attached which is typically set to 65 C. The entire system is controlled by a “TIMER” (H). The timer will determine when hot water should be generated. During the times that hot water is needed a signal is sent to the boiler via the thermostat. As long as the thermostat is below the cut off temperature (65C) the boiler will continue to heat and pump the water around the internal coil.

When the cylinder temperature reaches the cut off (65C) then it automatically disengages the boiler which simply turns off.

Summary

For a hot water vented system, the boiler only goes on if the timer indicates it is time for hot water AND the thermostat temperature has not been reached

How to remote control heating using Home Automation?

In order to control the hot water from a home automation system there is simply a need to replace the job of the thermostat with home automation capabilities.

Namely:

• A z-Wave Thermostat to measure the cylinder temperature. (must be able to work in the 65C range). Example fibaro external temperature sensor would work fine
• A z-Wave Relay that “enables” and “disables” the signal to the boiler. Any z-wave relay.
• The ability to control the relay remotely via a timer

NOTE: I do not know of a vendor that sells an external temperature sensor and switch in one unit so I have assumed that two z wave components would be needed

Enter "The Zipato climate widget"

The Zipato system already has a “climate” concept that could easily be used to control hot water since it already has a timer mechanism and temperature ranges.

The climate can trigger a device based on time of day and temperature needed. It is an ideal

vehicle to use for control of hot water.

The climate widget has:

• Ability to define temperature needed at specific half hour intervals during the day (four temperature ranges can be defined)
• Ability to be controlled (i.e. overridden) by the Zipato application
• Ability to be used in Rules

Problem with the climate widgetThere are two main issues currently with the climate widget

1. There is too much functionality in the widget for a hot water only implementation (!)
2. The widget does not work with a 65C temperature

The first issue can simply be ignored because more functionality is better than no functionality but the second issue is one that can only be solved by Zipato themselves.

My proposal to ZipaotoI believe the shortcoming of the climate control for this application could be solved by:

• Create a temperature “offset” for the climate that allows it to work with much larger temperatures
• Allow maximum temperature and minimum temperature to be set within each climate
• Creation of a new hot water widget (special type of climate)

I would hope that the second one is the easiest

Further enhancements

Most cylinders are also equipped with an electric immersion heater, typically rated at 3KW. They have their own thermostat built in to stop the water boiling inside the cylinder. There are various z-wave relays that are rated at 3KW which would allow the immersion heater to be remotely triggered as a “boost”.

If a new “hot water” widget is created then it can be equipped with an external “boost” mechanism that would allow the immersion heater to be used as a special boost in circumstances where the house owner did not wish to wait for the boiler to heat the water (which may take more time).

Conclusion

The above proposal can give the following advantages to the Ziapto customer:

• Ability to view the temperature of the hot water store
• Ability to control the temperature of the hot water store
• Ability to schedule hot water availability from app
• Ability to override hot water availability from app
• Ability to “boost” the hot water with remote control of the immersion heater relay.

I only own a Zipabox and Zipatab so do not know how competitive products implement this but the proposal above may well give Ziapto a unique proposition in the home automation market.

PLEASE VOTE for Zipato to consider this.

Thanks

/Marcus