Eight ways our home’s new heating controls can save energy and increase comfort

I was looking forward to switching on our central heating this winter.  Not just for warmth, but to try out the new digital wireless heating controls we’d fitted (see previous post).

I’ve counted eight ways the new controls save energy compared with the old controls. Upgrading the heating controls was a much more cost-effective way of cutting fuel bills than replacing the boiler!

Quantifying our energy savings due to the new controls will be difficult because we can’t compare “like with like”: we had cavity wall insulation installed last summer; we used the heating much more this past winter because it was a much colder than the previous years; and we were heating the whole house throughout the day throughout the coldest period, instead of only mornings and evenings as in previous years.  However I’m confident the new controls have saved energy in seven ways compared with the old controls.

Energy saving
The most important energy saving feature of the new Sundial RF² controls is its advanced TPI control: it stands for “Time Proportional and Integral”.  “Time Proportional” means the number of boiler firings per hour is regulated, while the length of each firing is calculated automatically to satisfy the demand for heat, but no more.  You can’t do that with simple on/off controls.  So the boiler doesn’t run unnecessarily and operates much more efficiently.  In our case, the boiler fires noticeably less often than it did previously under the old controls, which must also mean there’s less wear on boiler components.

That’s just the first way the new controls are saving energy. The “Integral” component of TPI control prevents variations around the set point – a disadvantage simple on/off controls.  It’s clear our living/dining room now has a very constant room temperature: the actual room temperature shown in the thermostat display is always exactly the “set” temperature. By comparison, the old controls allowed noticeable temperature swings of a couple of degrees either side of the set point.  This meant sometimes – especially at the coldest time of the year – we turned the old thermostat up a degree or so when we sensed the room temperature was uncomfortably low, only for the room to be too warm 20 minutes later.  That wasn’t good for our comfort or for energy efficiency.  Now we have a constant, comfortable temperature all the time, without any twiddling.

The temperature variations you get with the simple on/off controls (still used in many homes) are due to the delay after the temperature is sensed, before the hot water to the radiators stops or starts.  So, when the temperature falls, there’s a delay before the room starts to warm up. When the thermostat senses the set temperature has been reached, there’s another delay before the heat supply stops.  This cycle repeats, so the room temperature always swings around the set point.  The integral function in TPI smoothes this variation, so the room is soon at a steady even temperature with little variation – no more fiddling with the thermostat setting!

That’s already two ways we’re saving energy.

More accurate control
In addition, because the control system eliminates the temperature swings experienced with traditional on/off thermostats, and the new digital thermostat provides much more accurate temperature control, users can set the temperature a degree or so lower than previously to maintain comfort. This too saves energy: it’s said that lowering the set temperature by just one degree can provide fuel savings of 10 per cent.

Optimum start
The fourth way we are saving energy is thanks to a feature called “optimum start”. I’ve “enabled” this optional feature by selecting it in the Honeywell timer to maximise our energy savings.  The heating “start” time in the morning is now the time when we want to be warm, not when the boiler should fire for the first time.  Every day the controls sense how warm the room is already, then switch on the heating at the latest possible moment for us to be warm when we want. So we save energy by avoiding running the system earlier than necessary each day.

The optimum start option also provides the fifth way the new controls are saving energy: a built-in self learning facility recognises how the heating system reacts to control signals. This depends on the thermal characteristics of our home (room dimensions and heat loss through walls and windows) and also of the radiator heating system (how long the radiators take to warm the room, pipe lengths etc). The optimum start facility uses this to adjust the heating morning start time more precisely, so saving even more energy.

I’ve enabled another optional feature of the new controls – the sixth way they are saving energy.  This is called “optimum stop” and works in the opposite way to optimum start.  Each evening the controls automatically switch the heating off earlier than our preset bedtime if they determine there will be no noticeable temperature drop (one degree C, say).  So we save fuel while our comfort isn’t affected.  If the temperature drops by a discernable amount during this period, the controls bring the heating back on automatically to maintain comfort.

The seventh way the controls save energy is by timing the heating and hot water to come on only at the times when we need them.  The timer has four modes which can be set independently for space heating and hot water.  Presently we’re using the “Auto” mode which brings the heating and hot water on for up to two on/off periods per day, mornings and evenings.  You can program different time segments for each day of the week, if you wish.

As well as the “Auto” timer mode, there are three others: “Once” runs the heating daily from the first “on” times until the final “off” time, and “Continuous” runs the heating 24 hours a day. You can scroll through and select the four modes for space heating or hot water by pressing the appropriate button on the front of the timer.

When it’s set to Auto, should we decide we want heat during the day (after the morning heating period has finished) we simply press the override button on the timer.  That brings the heating on until the next “off” time is reached (at bedtime, in our case), without any changes to the normal heating programme.  If we decide we don’t want any more heating during the day, we press the override button and it goes off until the next programmed “on” time turns it on again.

One more hour, please
The timer has an “extra hour” button, which we can use when we want to keep the heating or hot water on for longer, without changing the programmed times.  You press it once for one extra hour, twice for two hours, and so on.  This potentially saves energy – the eighth way – because the override period is limited. So, for example, the heating doesn’t stay on all night wasting energy because you’ve forgotten to return the timer back to normal operation after staying up to watch a late night TV show.

There’s a similar feature – the “ECO button”, appropriately coloured green, on the wireless thermostat.  This provides timed setback. Conversely  you can use the thermostat to override the timer settings to give you an additional hour of heating, or multiples of an hour if you press it more than once.

We my not have been able to guarantee perfect health through the past winter, but our new heating controls provided a much more comfortable home, despite one of the coldest winters for many years.

Royer Slater
May 2011

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