If you're a regular reader of our blog then you'll know how much Vesternet love the Honeywell evohome system - so much so that we all use it in our own homes.
It's been around a year or so since we all installed it, so we thought that it was about time we posted an updated review - just in time for the new heating season in the UK!
Instead of writing this article ourselves however, we've invited a guest contributor to do so - Paul Ockenden from PC Pro magazine. Paul has also been using the Honeywell evohome system for quite some time and we welcome his views. It's always nice to get a third party opinion that matches our own :-)
Over to Paul, who has adapted this article from columns previously published in PC Pro ....
Smart Heating Choices
Are you perplexed by the confusing array of smart heating systems available these days? There’s Google’s Nest, the Hive system promoted by British Gas, and many other players such as Tado, Inspire, Netatmo, PassivSystems… the list goes on and on, with new players popping up on the various crowdfunding sites on an almost weekly basis.
Most of these devices are designed to replace the traditional thermostat on your wall, usually with some added intelligence: Perhaps having different temperatures at certain times of the day, and allowing you to turn the heating on and off from your phone while you’re out and about. Some have integration with other systems such as IFTTT, and increasingly they will even ‘learn’ how you live your life, and start to adjust the stored schedule to match this.
Most of these systems work a bit like a traditional heating thermostat in that there’s one controller, usually on a wall somewhere, with one thermostat for your whole house. But just think about that for a moment: Can you imagine living in a house with just a single light switch? One where all the lights go on and off at the same time?
For starters that would be an incredible waste of energy as you’d be lighting rooms that weren’t in use. But it would also be uncomfortable, as the person needing bright lights in the kitchen to do the cooking would inconvenience the person trying to watch TV in a dim living room, or the person trying to sleep off a migraine in a blacked-out bedroom. A single control would be bonkers, wouldn’t it?
So why do we accept the same the same thing from our heating systems? OK, thermostatic radiator valves (TRVs) can help in a small way, but they just set a target temperature for a specific room. They have no idea whether a room will be occupied at certain times of the day, or on certain days of the week. If you want your bedroom nice and toasty when you get out of bed in the morning, it’s going to stay toasty all day with a TRV.
We spend a fortune on energy saying light bulbs to reduce our electricity bills, but lighting accounts for less than ten percent of the energy costs in a typical house. Heating and hot water will usually make up over 80% of that bill, so surely that’s where we need to look for savings and improvements?
The best way to achieve this is through ‘zoning’. Splitting your home in separate areas, each having its own heating schedule. In fact some upmarket homes come with such a system already, with valves near the boiler opening and closing as required to heat different parts of the house. If you have a more ‘normal’ house though, perhaps with an ancient boiler and hot water system, there are systems available to allow you to retro-fit a zoning system.
These systems usually work by replacing your radiator valves with intelligent controllers, so that at different times of the day varying ‘set’ temperatures can be sent to the device.
There are several such systems on the market, although many have little niggles that work against them. Some need a wired connection to every radiator valve – in this day and age that’s bonkers. Others have one-way communication from a central controller to the radiator controls, just sending the set-point temperature. The problem with this is that the system doesn’t know when the house is up to temperature and all of the valves are closed. The boiler just keeps on churning away.
After a lot of research the system I eventually chose for my house was evohome from Honeywell.
The Honeywell evohome system consists of a central controller device, special TRV heads that you fit to every radiator, plus a few other optional bits and bobs. Why did I go for evohome over the other systems available? Well, mainly because it’s a mature system. The evohome Controller is now on its third generation, although it’s actually even older than that as its roots lie with an even earlier system called Hometronic. Even the Honeywell radiator control devices are now on their second generation. Other, newer systems are still very V1.0, and have the associated problems that V1.0 devices always seem to have.
At the heart of the system is the evohome Controller. This talks wirelessly (using 868MHz) to all of the other bits and pieces. These can either be sensors (thermometers, for example) or actuators (the things that turn radiators on and off, relays, etc.). Some devices contain both – the radiator controllers for example, as well as turning the rads on and off, also contain a temperature sensor. And the comms is two way, which is important in two respects. Firstly it means that on a TRV or a room thermostat you can make a local change and this is reported back to the evohome Controller. The second reason for the back-channel is that the devices can report their demand for heat, meaning that the boiler only needs to fire up when at least one radiator is calling for it.
The evohome system is ideally suited to older properties with old fashioned boilers and radiators, although it can also cope with things like wet underfloor heating. If you have a system with a stored hot water tank heated indirectly by your boiler it’ll also control that.
Let’s have a more detailed look at each of the various components of the system. The Controller device has a colour touch screen. It’s the main heart of the system, and allows you to see and control the temperature in every room (or more correctly each zone – you can put several rooms into one zone if it makes like easier), and also your hot water. For each zone you can set different target temperatures for various times of the day (and indeed different days of the week). You can also over-ride the temperature in any zone for a particular period of time, and there’s a number of ‘quick actions’ available that’ll do things such as turn the whole house down a few degrees, or set the system into ‘working from home’ mode where it’ll treat a weekday as if it was a weekend.
There are two mounting options with the controller – you can either have it on a table-top stand or attached to the wall. It contains a rechargeable battery so can be removed from the wall or table for short periods, but it’ll start to beep if you keep it away from the mains for too long.
As well as the 868MHz radio for talking to the various evohome components, the controller also has 2.4GHz Wi-Fi comms for talking to your broadband router. These talk to Honeywell’s cloud infrastructure, and enable you to use smartphone apps, plus there’s an API (not well documented, but plenty of example code on Github) and integration coming with other systems such as SmartThings. The smartphone and tablet apps pretty much mirror the facilities available via the evohome Controller.
In each room you’ll need to control the heat source, which in most cases will be a radiator. This is done using special HR92 radiator controllers. If you already have thermostatic radiator valves you can simply remove the existing head and replace them with the HR92. Most brands of TRV are supported, although with of a few of them you’ll need to use an adapter.
The HR92 senses the temperature in the room (it’s designed to measure the temperature of the updraft that occurs around the edge of a room), and tries to maintain the set temperature. It does this by opening the radiator valve in a proportional manner (not just on or off), and by demanding heat from the boiler, when needed – more on that in a moment. There’s a large LCD display on the HR92 which displays the current set temperature for the zone – you can change this if you want to show the room temperature instead. Using a rotary dial you can also override the temperature set by the evohome Controller – any local adjustment you make will apply until the next scheduled temperature change.
I’ve been very impressed with how isolated the temperature sensing of the HR92s appears to be, considering they are attached to hot pipes and sitting right next to a bloody great heat source. Even when a radiator is extremely hot the white body of the device seems to remain at room temperature. The other impressive thing is the battery life – there’s two AA batteries inside the HR92, and despite all of the mechanical opening and closing, the RF comms and keeping the LCD display updated, normal alkaline batteries will last around two years (you get a notification on the evohome Controller when they need to be replaced).
You might have multiple heat sources in a zone, and evohome gives some flexibility as to how these are treated. Each can work in isolation from the others, or one radiator (or other sensor – more in a moment) can be the master, controlling all of the radiators or other forms of heat. The latter sometimes works better if you have one large room with several radiators, or an open plan space, and is the default behaviour, whereas the former is designed for where you have multiple rooms in a single zone. Having played with both I reckon that even for large open spaces the ‘multi room’ option usually works best.
In situations where you have a radiator behind a sofa or a bed, say, or in one of those strange radiator cabinets that were fashionable a few years back, then the sensor in the HR92 obviously won’t give you a true reflection of the temperature in the room. In this case you can use an external sensor in the room. There are two main options available, and like the radiator controllers they are completely wireless. There’s a stylish round wall mounted thermostat called the Y87RF (I wonder who thinks of these snappy names – it is also known as the Single Zone Thermostat but that’s confusing when used in an evohome setup), or a more utilitarian looking device known as the DT92E. Both have fairly large display and they show the current room temperature. With the former you can adjust the zone temperature up or down by rotating a large bezel around the display. The DT92E has more conventional push buttons. Actually, it goes two steps further than its stylish round cousin by offering an ‘eco’ button which you can use to change the temperature of the zone for a number of hours (this is done independently of the Eco settings available on the evohome Controller). It also has a button that turns the whole zone off.
Another advantage the DT92E has over the Y87RF is that it comes with a table stand as well as a wall mounting facility. The round thermostat is wall mount only. It comes with screws and rawlplugs in the box, but if your walls are reasonably sound I’ve found that my old favourite VHB tape works really well.
If you’re the kind of person who likes to ‘fiddle’ then of the two room thermostats the DT92E is probably the better bet, but if you just want something like looks stylish on the wall I’d thoroughly recommend the Y87RF.
Honeywell’s installer manual is really good and well thought out, and covers most of the possible types of installation. When it comes to how the system interfaces with the boiler there are a few different options. My house has what’s known as an S-Plan heating and hot water system – there are separate motorised valves for the heating and hot water circuits, and then a feed from each of these fires up the boiler once the valve is fully open. With conventional heating controls these valves would be driven from a time clock and a room thermostat.
When retro-fitting evohome you bypass the old time clock and thermostat, and feed power to the two way valves via a small wall mounted relay box known as a BDR91. It’s a receiver which receives commends from the evohome Controller when heat from the boiler is needed, either to heat a room or for the hot water. By the way, the temperature of the hot water tank is sensed using yet another battery powered wireless sensor.
In my house I have 14 radiator valves, both types of room stat, the hot water sensor, two BDR91s, plus of course the evohome Controller itself. You’d think that would be a lot of RF flying around, and that there would be either interference or collisions, but that’s not the case at all. The RF side of things has been designed to work on a one percent principal. 1% communication, 99% silent. And the timings of the various devices are staggered, so there’s never any noticeable wireless congestion. I’ve watched the comms using my trusty RF scanner and it all seems to happen extremely quickly.
It’s easy to install the system yourself. There’s no plumbing (unless you don’t already have TRVs), but if you’re scared of electricity you might just need a sparky to wire in the BDR91s.
Is it worth it?
So, the big question is, is it worth it? Fitting an evohome system isn’t exactly cheap. But then again, neither are fuel prices. Honeywell reckons the system will typically save around 40% on your fuel bills. In my first year of operation I’ve found it to be closer to 25%.
But even if you ignore the economics, the big thing for me is comfort. With my old system a radiator would be either on full blast or stone cold. Room temperatures would cycle too. And as you walked around the house there would be pockets that were too warm or too cold. The evohome system has changed all of that. Radiators are now warm – just warm enough to hold a room at the temperature needed. There’s no more heating up and cooling down as the heating cycles on and off, and because of this I’m able to set a lower temperature than before, knowing that it won’t fall below that. The whole house feels much more comfortable.
In the past I’ve always laughed at people who say things such as “It’ll soon be time to turn the heating on” when the days start to get colder. For me, there was never any switching the heating on or off – I had a thermostat on the wall which did that for me. When the weather got warmer the heating would stay off, and then as the days got colder it would come on again. All by itself, completely automatically. No manual intervention required.
However, since having evohome installed, which provides a much tighter control over temperatures, I’ve found that during the Spring and Autumn weeks although it’s great that the heating comes on all by itself, I don’t want it quite as hot as I would during the depths of Winter. It’s at that time of year when nice warm sunny days mean cloudless skies, which in turn means that the night-times can be rather cold. So on days like these when the days are OK but there’s a bit of a chill in the mornings and evenings, it’s nice to warm things up a bit. However, I’ve discovered that heating the house up to our usual Winter temperature of 20 – 23 degrees (depending on the room) actually feels slightly too hot at these times of the year.
I think it’s partly psychological. After a nice warm day it’s nice that the evenings are a bit cooler, you just don’t want them too cool. A bit of heating is nice, but you only need the system to take the edge off a bit, without coming on full-blast. Perhaps evohome is spoiling me, making me seek level of comfort that I simply hadn’t contemplated before.
Thankfully, the system has a special ‘Eco’ mode, which temporarily over-rides the temperature for all of the zones, reducing them by three degrees. That seems just about perfect for the sunnier days during these transitional weeks, and makes the living space much more comfortable. But of course, selecting ‘eco’ mode is a manual process, so I’ve joined the ranks of the ‘manual intervention’ brigade. Yes, the same people that I’ve previously laughed at. And that just won’t do!
As you’ve probably guessed by now, there’s a solution at hand, and that comes in the shape of IFTTT, because Honeywell has created an IFTTT channel for evohome.
There are no triggers right now, which is a shame because you can’t do something like “if the loft is too warm lower the blinds on the Velux windows”.
What you can do though is turn your hot water on or off, over-ride the temperature in a zone, either permanently or for a number of hours, or enable/disable one of the evohome ‘Quick Actions’, such as the ‘drop everything by three degrees’ Eco mode that I mentioned earlier.
The simplest way to use this is to combine it with the Weather channel, where one of the triggers is ‘Current Conditions’, which returns one of four values, Rain, Snow, Cloudy or Clear. You actually need three recipes (if we ignore snow, which is unlikely during these transitional weeks). So if the current condition changes to clear (i.e. if it’s a sunny day) then turn on Eco mode, and if it becomes either cloudy or rain turn Eco mode off. That way, on the warm ‘Indian Summer’ days you get a small amount of heating, whereas on cold, wet, dreary days the heating comes on properly.
Phew, that's a great read and as mentioned at the start of the article it's great to see such enthusiasm for Honeywell evohome that matches our own!
We're hoping to see more articles from Paul in the future, in the meantime check out the full range of Honeywell evohome here and be sure to read our full Heating guide for a summary of your Smart Home heating options.
Bye for now.