Climate Control

Here in the UK, most houses now have a 'central heating' system. These typically use a single boiler to provide space heating and hot water. Most homes also have a single thermostat, located in the hallway. Some have two zones for upstairs and downstairs control. The thermostat typically drives a simple controller with pre-set times for the space heating and hot water to go on and off. All in all, it is pretty basic and horribly inefficient.

The linkage of hot water heating to space heating just doesn't make sense in any country. Here in the UK, we have long spring/summer periods where we never want to have the heating on but, the requirement for hot water is pretty much a constant throughout the year. In our current home, we physically turn off the central heating on the controller during the warmer months.

IMI LP241 controller
Our current home has an IMI LP241 combined heating and water controller. The system in our current home links the hot water and heating system, via a hot water cylinder that operates using mains water pressure.

IMI LP241 controller open
It has a pull-down flap to to reveal some basic control buttons. It can independently control two on/off time slots for each day of the week. If the heating is on, the hot water is also on. It doesn't adjust the clock automatically to handle British Summer Time. There isn't even a '+1 hour' button.

LG air-conditioning unit
Very few UK homes have the ability to cool rooms and most of those that do, have a retro-fit system installed into a single room.

The End Goal

Before you try to update an existing system or even design the ideal system, you need to have a clear view of the 'end goal'. This is a clear view of what you want your heating, cooling and ventilation system to be able to do and why. The reason for this is that the path taken to reach this goal will be very different to the one taken whilst performing incremental updates in isolation.

Our ideal situation would be one where our Smart Home:

  • Just knows the temperature required in each room at any given time of day, depending on whether we are in, out or away.
  • Is as efficient as possible, whilst also being responsive.
  • Requires no manual intervention or control in normal use and is a silent, invisible, 'zero touch' system.
  • Learns from our behaviour and detected presence and occupancy.
  • Understands the structure of our home, the rooms within it and the implications of interconnecting doors being left open.
  • Is aware of environmental conditions (location, weather, time zone, time, etc.).
  • Is optimised for the characteristics of our home (insulation, room volumes, heating system output, etc.).

These goals fit perfectly with our Smart Home philosophy and it is with these goals in mind, that we are planning our heating and cooling system design:

Zones & Rooms

With the end goal in mind, it is very clear that we need a system that can model all of the zones (rooms) in our home. In addition, it needs to be aware of the temperature in each zone, the required (target) temperature in each zone, whether each zone is in use and what heating and cooling is available in each room. In an ideal world it would also know how the zones were connected together (are there doors and are they open or closed), if they have windows (and whether they are open or closed) and whether ventilation systems exist to move air warm or cool air between zones. In addition, there may also be other sources of heating (e.g. a wood burning stove) in a room for aesthetic reasons and a 'feel good' factor.

It doesn't take a scientist to see that this holistic view of the home results in a more complex system than the current single zone (or even twin zone) heating system found in most homes today but, to achieve maximum comfort and efficiency. It is our view that this is the correct path to take and the complexity does not necessarily come with an associated cost, as we plan to show.

Insulation

The first law of home energy conservation is to insulate! It goes without saying that our plans are based on an exceptionally well insulated home.

Cooling

The decision to heat or cool a home in the UK is actually quite a simple one. The temperate climate means that the two functions are never required at the same time of year. Typically, we don't have our heating switched on at all during the months of May through to (and including) October. The use of a cooling system would be limited to one, maybe two months in at the peak of the summer, if required at all.

The most efficient cooling system or heating system is one that is not switched on. As such, we plan the ability to switch both space heating and cooling functions off altogether. This would not affect the ability of the systems to exercise themselves though.

Occupancy

With minimal cost (less than £200) we have added PIR sensors in every room and door contact sensors on every internal and external door. These have been installed in our current home (retro-fitted) as part of a wider Smart Home security system and to provide accurate and timely presence and occupancy information. This approach has proven to be extremely accurate and timely in determining if our home and its various rooms are occupied.

Within the scope of a typical heating and cooling system alone, this may not make a lot of sense but, within our wider Smart Home view it makes perfect sense, whilst providing the foundations of an intelligent and efficient climate control system.

Thermostats

Existing Honeywell thermostat
This is the thermostat that is installed in our current home. It is located in the entrance hall about 3m from the front door. The temperature in this hallway bears no relationship to the temperature in the rest of the house.

When central heating systems were first being installed, the concept of a thermostat made a lot of sense. It was a single, cheap component that even came with a fairly standard interface. It was an incredibly simple control loop but, it stopped the heating just coming on and staying on. Over the years, as heating and cooling technology moved on, the concept of having the single point in your home controlling the temperature of the whole house stuck.

If you think about it for a moment, the concept of a centralised thermostat is madness. Not only does a typical house have a heating system that actively introduces cold spots and hot spots but, the whole house conforms to the basic laws of physics. Warm air rises and you get temperature gradients between rooms and the outside of the house. A single thermostat in a modern home is working on the basis of a statistical sample of one. It isn't even safe to say that it sees an average temperature.

The location, height and house layout will make a huge difference to how a house is heated. Opening just one door, say the front door into the hallway where the thermostat is located, will result in massive heat injection into the whole house.

Let us put it another way ... Would you use a single 'smart' thermostat to control the heating in an office block? So why employ the same basic principles to your home?

Smart Thermostats

Nest thermostat
Whilst smart thermostats like the Nest thermostat are a valuable incremental step in isolation, they simple are not a useful device when looked at in the context of our end goal. They are designed to fit, where the existing thermostat is located (in an often non-ideal location), they have limited occupancy detection and understanding and a single temperature sensor for the whole house.

Whilst they often have some clever features and technology, these kinds of devices are also highly visible and encourage you to play with them. Many also have an associated iPhone app that further encourages this behaviour. This simply does fit with our stated philosophy of invisible intelligence that just works in the background. The Nest thermostat is essentially a closed system too, its PIR and temperature sensor can be used for one thing only. Put simply, there is no place for this kind of device in a proper Smart Home.

Whether they are 'smart' or not, thermostats get touched and played with by family members and guests, whether it be by accident or simply curiosity. Not having a device like this on display is a benefit.

Temperature Sensors

For temperature sensors to work well, there need to be lots of them and they need to be located in the right place(s) and at the right height. This means one per zone/room as a minimum. They also need to be accurate and responsive to temperature changes. That said, the temperature sensors are only as useful as the controller that sits behind them.

Taking the holistic view, we also require our temperature sensors to be multi-functional. In our Smart Home, we envisage some of them being powered, Z-Wave nodes, acting as relay nodes and forming the backbone of a multi-function Z-Wave network.

Temperature sensors have more than one use. We also use them to detect abnormal temperatures as part of our home safety system and we also monitor rate of temperature rise, to look for abnormal temperature rises. This requires them to have low latency.

Thermostatic Valves

Thermostatic radiator valve
Thermostatic radiator valves are a cheap, 'quick fix' upgrade to improve the efficiency of existing central heating systems. They have an actuator that responds to preset heat levels and gradually close the valve as they sense the temperature rising around them. One problem with this approach is that the valves can be quite noisy. They also react to the temperature of the air at their location and since they are attached to the radiator itself, this is a compromised location. It is further compromised by being very low to the floor.

In an existing home, these are a fairly crude way to improve the efficiency of a heating system but they do improve efficiency slightly. Many heating systems are balanced and these types of valves can upset that balance, having an impact on the heating in other rooms.

Wireless Radiator Valves

Wireless radiator valve
Wireless radiator valve overcome many of the limitations of thermostatic radiator valves by separating the valve actuator and the temperature sensor. Typically are 'clip on' devices that replace the dumb actuator with some electronics and a solenoid. They are remotely controlled using a wireless technology such as Z-Wave.

In an existing home, these are a valid step forward but, in a new build it makes much more sense to have the zone control at the boiler or heat source.

Heaters & Heat Sources

Most homes have other sources of heating in them such as cookers, other appliances and even people. We want out climate control system to know about these things and adapt its behaviour accordingly. Our smart home already does people counting but, we want to add awareness of appliances like cookers being on. This involves monitoring electicity usage and using device characterisation based on analysis of the loads.

Air Movement & Ventilation

Air movement within and between rooms is an important aspect of climate control. Circulating air within a room has a mixing effect, which removes hot spots and cold spots. This is particularly important in spaces that are also heated by the sun, e.g. a conservatory. Too much movement of the air will introduce a noticable 'wind chill' effect though.

The Exhale Bladeless ceiling fan is an interesting take on the air movement issue:

Latency

Underfloor heating systems are more energy efficient, quieter, maintain a comfortable humidity and keep temperatures more stable but, they suffer from latency. This means that they take a long time to heat up and cool down. In order to have a warm bathroom when you wake up, you need to switch the bathroom heating on hours before you first walk into it. If your heating controller is not designed with this latency in mind, it will also keep heating until the required temperature is met and then overshoot (over heat) the room as heat continues to radiate out.

We have written a more detailed article on latency in the smart home.

Stiction

Central heating systems left dormant for too long suffer from excessive stiction. Sediment will settle in pipework and pumps will stick. The elements of a house heating system need to be regularly 'exercised', even if there are not made to do any real work.

The process of exercising components needs to be designed into any climate control system.

Controller

So how are we going to implement this? This is work in progress but, our current thinking is to split the climate control in to two separate elements. This is essentially a natural split between software and hardware but, it's not quite that simple:

  1. The first part is the intelligent control element and basically determines the target temperature required in each room, based on all of the factors previously. We have already built this and have in running and in testing in our current home as a generic controller project.
  2. The second part is currently in development and test in our current home. This is the 'actuator' that translates the requested temperatures into intelligent and predictive heating and cooling control, driving the 'hardware' in an optimally efficient fashion.

Monitoring

As part of our Home Control System (HCS) we have extensive logging capability, that allows us to monitor how well the controller and sensors are working. This is not something you would want to do regularly though.

User Interfaces

Whenever you see home automation and climate control mentioned in the same sentence, you generally see a picture of a Smartphone app. It's usually alongside a photo of a very nice looking thermostat. Hopefully, we have shown how redundant a thermostat is in a modern Smart Home and thus we don't have a requirement for such things.

Beyond the initial configuration of the system, to determine target temperatures in each zone or room, we only foresee the following user interface elements being required:

  • The temperature sensors in each room will be subtle and very compact but, will feature an OLED display of the current temperature, which is only displayed when the temperature sensor is touched. This is purely to satisfy that very human urge to validate what we generally already know.
  • All other queries and requests will be achieved via our natural language interface.

So in summary, we don't plan to have any day to day user interfaces for climate control and we certainly don't plan to have an app. Our home knows when we are in, out or away and learns and adapts accordingly. No playing, no tweaking, just trust in the system to get on with its job, silently and invisibly in the background.

Costs

It's hard to isolate the costs associated with the climate control aspects of our planned next house, because our holistic approach means that components generally support mulitple features and functions. To put it into perspective though, we envisage spending less than £2000 on our complete Smart Home system. This includes pretty much all of the elements covered as projects but, it doesn't include the entertainment elements (which are many times this).

Further Reading

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