Stop Cooling an Empty House: The Next Smart-Home Saving

We’ve learnt to control our heating. Now perhaps our homes need to learn how to manage summer.

For years, the smart-home conversation in Britain has largely been about winter.

Smart thermostats turn the heating down when we go out. Individual radiator controls stop us heating unused rooms. Timers prevent boilers and heat pumps running unnecessarily. Some systems even learn when we normally arrive home and make sure the house is comfortable just before we walk through the door.

It makes perfect sense.

So why, as our summers become hotter, do we often approach cooling in a completely different way?

A room becomes unbearably warm, so we switch on a fan.

If that does not work, perhaps we buy a portable air-conditioning unit.

Then we leave it running while we cook dinner downstairs, go shopping, sit in the garden or even leave the house entirely.

We would think twice about leaving the central heating blasting away in an empty house in January.

Perhaps we should start thinking the same way about cooling in August.

And there is an even more important point.

The cheapest heat to remove from a house is the heat that never entered it in the first place.

That means the smart summer home should not simply be good at cooling itself.

It should be good at preventing itself from becoming hot.

The Summer Version of a Smart Thermostat

Imagine leaving home at 8.30 in the morning.

You are going to be out until 5.00 pm.

Traditional thinking might be:

“I want the house cool when I come home, so I’ll leave the air conditioning running.”

Smart-home thinking should be very different.

The house knows nobody is home.

The temperature outside starts climbing.

Sunlight begins pouring through the large west-facing windows.

Instead of immediately switching on mechanical cooling, the house responds in stages.

At 11.00 am, the external blinds close.

At midday, selected internal blinds close as well.

Windows that were open during the cool morning are closed once the outside air becomes hotter than the indoor air.

Ceiling fans and portable fans remain off because nobody is there to feel them.

Smart plugs turn unnecessary electronics off.

The heat pump does nothing.

Then, perhaps shortly before you are due home, the system looks again at the temperature.

If cooling is actually necessary, it starts then.

That is much closer to the way we have learnt to manage winter heating.

And importantly, much of it can already be achieved with relatively inexpensive smart-home equipment.

First Rule: Don't Cool People Who Aren't There

This sounds obvious, but it is worth understanding what different cooling devices actually do.

Fans don't really cool rooms

A fan mainly cools people, not houses.

Moving air increases evaporation from our skin and improves heat transfer from the body. We therefore feel cooler.

But the fan motor itself actually adds a small amount of heat to the room.

Consequently, leaving a fan running in an empty bedroom for three hours so that the room will be cool when you return achieves almost nothing useful.

If nobody is in the room:

switch the fan off.

A smart plug, occupancy sensor or home-automation routine can do this automatically.

For example:

IF bedroom unoccupied for 15 minutes
THEN switch fan off.

Simple.

Cheap.

Potentially useful throughout every summer.

Air Conditioning Is Different

Air conditioning really does remove heat from indoor air and transfer it outside.

But that makes running it unnecessarily much more expensive than running a fan.

The same is true if an air-source heat pump can operate in cooling mode.

Here the principle should resemble intelligent heating.

Instead of:

Cooling on = all afternoon

we might use:

Cooling enabled only when:

somebody is home;
indoor temperature exceeds a chosen level;
passive cooling cannot maintain comfort;
doors and windows are appropriately positioned;
electricity conditions make running the system sensible.

That final point becomes particularly interesting if the house has solar panels.

Cooling When the Sun Is Paying for It

This is something I find particularly interesting because my own home already has solar panels, substantial battery storage and a heat pump.

Summer presents an unusual opportunity.

The conditions that create the cooling problem — strong sunshine — can simultaneously provide some of the electricity needed to solve it.

Imagine the house reaches 25°C at 1.00 pm.

Solar generation is high.

The battery is already substantially charged.

Rather than waiting until 6.00 pm, when the sun is lower and everyone has returned home, the automation could gently cool the house during the afternoon using surplus solar electricity.

The walls, floors and furniture effectively become a small thermal store.

This is sometimes called pre-cooling.

You are not trying to turn the house into a refrigerator.

Perhaps you simply bring it down from 25°C to 22°C or 23°C while solar electricity is plentiful.

Then the building slowly warms later.

Depending on the house, that may reduce or delay evening cooling demand.

Smart-home energy management becomes particularly interesting when electricity generation, battery storage, weather forecasts, occupancy and temperature measurements can all interact.

But Before Cooling the House, Stop Heating It

This is probably the most important change in thinking.

We often wait for the house to become hot and then try to remove the heat.

It is rather like leaving every window open in January and compensating by turning the heating up.

Sunlight passing through glass can deliver a surprising amount of energy into a room.

Once that solar energy has warmed the:

floor;
furniture;
walls;
worktops;
carpets;
beds;

the house has effectively stored it.

You then have to get rid of that heat again.

So perhaps the first smart summer appliance should not be the air conditioner.

It should be the blind.

Automated Blinds Could Become Much More Important

Motorised blinds used to feel rather luxurious.

You pressed a button and the curtains dramatically opened.

Very impressive.

But increasingly I think automated shading could become an energy-saving technology rather than simply a gadget.

Consider a large west-facing window.

During winter, afternoon sunshine may be welcome.

During a hot August afternoon it may be exactly what you do not want.

A smart system could respond differently depending on conditions.

Winter

Sun shining + room cool
= open blind

Free solar heating.

Summer

Sun shining + room already warm
= close blind

Prevent overheating.

That simple distinction changes blinds from decoration into part of the home's environmental control system.

External Shading Is Even Better

There is an important physical difference between internal and external shading.

With an internal blind, sunlight has already passed through the glass before hitting the blind.

Some of that energy therefore remains inside.

With an external shutter, awning or blind, much more of the sunlight can be intercepted before it enters the building.

That is why traditional architecture in hotter countries so often uses:

shutters;
verandas;
awnings;
deep window recesses;
pergolas;
overhanging roofs.

British houses may increasingly need to borrow some of those ideas.

And smart technology could automate them.

An awning could retract automatically during strong winds.

External blinds could close when solar intensity and indoor temperature both rise.

Shutters could reopen in the evening.

This is not futuristic technology.

The clever part is simply connecting the sensors to the decisions.

Your House Needs More Than One Thermometer

Many homes have one thermostat.

Usually it is in the hallway.

That might have been acceptable when its main job was deciding whether the boiler should switch on.

It is much less useful when trying to understand summer overheating.

Upstairs may be 28°C while downstairs is 23°C.

A south-facing bedroom may be far hotter than a north-facing room.

The conservatory could be approaching greenhouse temperatures while the rest of the house remains comfortable.

A network of relatively inexpensive temperature sensors can reveal what is actually happening.

You might measure:

living room;
kitchen;
main bedroom;
loft;
conservatory;
outside shaded temperature.

Suddenly the house has information.

And once it has information, automation becomes possible.

Indoor Temperature Alone Isn't Enough

Here is where smart summer ventilation becomes much more interesting.

Suppose your bedroom is 25°C.

Should the window open?

Possibly.

But what if the outdoor temperature is 30°C?

Opening the window may make matters worse.

Now imagine the bedroom is still 25°C at 10.00 pm but the outdoor temperature has fallen to 18°C.

Opening the window becomes extremely useful.

So the decision should really be:

Is it cooler outside than inside?

Something as simple as:

IF indoor temperature > 24°C
AND outdoor temperature < indoor temperature
THEN ventilation recommended

could transform how the house behaves.

Open the House at Night, Close It During the Day

During prolonged hot weather, one of the simplest strategies can be night cooling.

When evening temperatures fall:

open suitable windows;
create cross ventilation;
release stored heat;
cool the building fabric.

Then, before the outside temperature climbs the following morning:

close windows;
close appropriate blinds;
reduce solar gain;
keep cooler air inside.

The house becomes somewhat like a thermal flask.

The difficulty is remembering to do it.

Smart homes are very good at remembering repetitive jobs.

Could Windows Open Themselves?

Technically, yes.

Motorised window actuators already exist.

But I suspect most homes do not need every window converted into a computer-controlled machine.

Smart technology does not have to mean maximum automation.

A much cheaper system could simply send a message:

Outside temperature has fallen below bedroom temperature — consider opening upstairs windows.

Or:

Outdoor temperature is now higher than indoor temperature — close windows to retain cooler air.

The human remains part of the control system.

Sometimes that is the most sensible smart-home solution of all.

Be Careful About Automatically Opening Windows

There are obvious complications.

A smart system must consider:

security;
rain;
pets;
children;
strong winds;
insects;
occupants who may not want draughts.

Leaving downstairs windows automatically opening while nobody is home would clearly be unwise.

So automation does not mean blindly connecting every measurement to a motor.

Good smart homes should understand context.

Cross Ventilation Beats Randomly Opening Windows

Opening one window may achieve surprisingly little.

Opening windows on opposite sides of a house can create a flow path.

Cooler air enters one side.

Warmer air leaves the other.

Staircases can also create a natural vertical pathway because warm air tends to rise.

In some houses, opening a lower window on the shaded side and an upper window elsewhere can encourage useful airflow.

This is another area where simple measurements can teach us something.

Place temperature sensors around the house and experiment.

Try:

all windows closed;
one window open;
opposite windows open;
upstairs and downstairs windows open.

Record the temperature every ten minutes.

You may discover that your house has a surprisingly effective natural ventilation pattern.

Smart Plugs: Small Savings That Add Up

There is another source of summer heat we often forget.

Almost every electrical appliance eventually turns electricity into heat.

Computers.

Televisions.

Games consoles.

Chargers.

Lighting.

Printers.

Network equipment.

Kitchen appliances.

They may individually seem insignificant.

But during a very hot afternoon, why add unnecessary heat to the building?

A smart plug can automatically turn off equipment that does not need to run.

For example:

Study unoccupied + computer equipment idle
= peripherals off

Or:

Television area unoccupied after midnight
= entertainment equipment off

The electricity saving may be modest.

But during hot weather there is a double benefit.

You avoid consuming electricity and avoid producing heat that might later need removing.

Even Lighting Matters

Traditional incandescent lamps were essentially tiny heaters that happened to produce some light.

LED lighting is enormously better.

But LEDs still produce heat.

During winter that hardly matters.

During very hot weather there is little reason to leave unnecessary lighting operating in an empty room.

Occupancy sensors can solve that automatically.

Again, we return to the same summer rule:

Don't cool heat that you didn't need to create.

What About Portable Air Conditioners?

Portable air-conditioning units are becoming increasingly tempting during heatwaves.

They can certainly make a room more comfortable.

But they should probably be considered one of the later stages of a cooling strategy rather than the first.

Before switching one on, ask:

Can direct sunlight be blocked?
Could the room be ventilated while it is cooler outside?
Are unnecessary appliances running?
Could a fan provide sufficient personal cooling?
Is the room actually occupied?
Could the cooling be delayed until electricity is cheaper or solar generation higher?

Only after dealing with those questions should active cooling necessarily become the answer.

One Particularly Important Problem: The Exhaust Hose

Many portable air conditioners use a single exhaust hose through a window.

The machine removes heat from the room and blows hot air outside.

But because air is being expelled from the room, replacement air has to enter somewhere.

That replacement air may itself be hot.

Poorly sealed window openings can make matters even worse.

So if using portable air conditioning, make sure the exhaust arrangement is properly installed and the opening around it is sealed as effectively as practical.

Otherwise you can end up simultaneously cooling the room and drawing more warm air into it.

Heat Pumps May Change the Equation

Many people think of a heat pump purely as a replacement for a gas boiler.

But some heat-pump systems can provide cooling as well as heating, depending on their design and installation.

That presents an interesting possibility.

Instead of installing separate air conditioning, the same broad energy system that keeps the house warm in winter may help manage summer temperatures.

But again, the objective should not be:

"It's summer, switch cooling on."

It should be:

"Use the minimum active cooling required after passive measures have done as much as possible."

That distinction matters.

Build a Cooling Hierarchy

I think the smart summer house needs a simple hierarchy.

Stage 1 — Prevent heat entering

Use:

external shading;
blinds;
curtains;
awnings;
shutters;
shade from trees and vegetation.

Stage 2 — Reduce internal heat

Turn off:

unnecessary lighting;
computers;
entertainment equipment;
other avoidable electrical loads.

Stage 3 — Use natural ventilation

But only when outdoor conditions make it useful.

Stage 4 — Cool the person

Use fans when people are actually present.

Stage 5 — Cool the building mechanically

Use heat pumps or air conditioning when genuinely needed.

That order could save considerable energy compared with simply reaching for the air conditioner every time the temperature rises.

Occupancy Is the Missing Ingredient

The biggest improvement may come from combining environmental sensors with occupancy detection.

Suppose a spare bedroom reaches 27°C.

Does it matter?

If nobody is going to use it for three days, perhaps not very much.

A living room containing four people is different.

A home office being used all afternoon is different again.

So perhaps smart cooling should not ask:

"Is this room hot?"

It should ask:

"Is this room hot, occupied and worth cooling?"

That one extra piece of information could prevent a great deal of unnecessary energy consumption.

Different Rooms Need Different Rules

One of the problems with traditional central heating is treating the entire building as though every room has the same requirements.

We have gradually improved that with thermostatic radiator valves and zoned heating.

Cooling should probably develop in the same direction.

Bedroom

Priority: comfortable sleeping temperature.

Possible strategy: strong evening ventilation and overnight cooling.

Living room

Priority: afternoon and evening occupation.

Possible strategy: automated shading before peak sunshine.

Kitchen

Priority: control internal heat.

Cooking itself can add substantial heat.

Home office

Priority: daytime comfort.

Possible strategy: targeted fan or local cooling while occupied.

Spare bedroom

Priority: minimal intervention unless needed.

Suddenly we are not cooling a house.

We are managing individual environments.

Let the Weather Forecast Join the Smart Home

A truly intelligent system could go one step further.

Suppose tomorrow is forecast to be much hotter than today.

The home could prepare.

During the preceding night it might encourage more ventilation.

Morning blinds could close earlier.

Battery charging strategies could change.

Cooling could happen earlier while solar generation is plentiful.

Conversely, if tomorrow will be cool and cloudy, there may be no reason to aggressively pre-cool the building at all.

The home begins to behave proactively rather than reactively.

The £50 Version of the Smart Summer Home

This does not require a huge automation project.

A very basic experiment might begin with:

two or three inexpensive temperature sensors;
one outdoor sensor;
a few smart plugs;
existing blinds or curtains;
a smartphone.

You could monitor the house manually for a week.

Record:

outside temperature;
indoor temperature;
which windows are open;
blind positions;
sunshine;
room occupancy.

Very quickly you may start noticing patterns.

Perhaps the upstairs bedroom overheats every afternoon.

Perhaps closing one blind at lunchtime makes a substantial difference.

Perhaps opening windows at 4.00 pm actually warms the house because the outdoor air is still hotter.

You do not necessarily need artificial intelligence.

Sometimes measurement itself changes behaviour.

The £500 Version

Take things further and you could add:

motorised blinds;
more temperature sensors;
smart thermostatic control;
automated fans;
smart plugs;
door and window sensors;
solar-generation information;
battery state-of-charge monitoring.

Now genuine automation becomes possible.

The Fully Integrated Version

At the other extreme, imagine a house measuring:

indoor temperature;
outdoor temperature;
humidity;
sunlight;
weather forecast;
solar generation;
electricity price;
battery charge;
window position;
room occupancy.

The control system might decide:

10.15 am

South-facing room warming rapidly.

Close blind.

12.30 pm

Outdoor temperature now exceeds indoor temperature.

Recommend closing windows.

2.00 pm

Solar export high.

Battery 95%.

Living room expected to be occupied at 5.00 pm.

Pre-cool slightly.

7.30 pm

Outdoor temperature below indoor temperature.

Disable mechanical cooling.

Recommend natural ventilation.

That is much closer to what I think the genuinely useful smart home will eventually look like.

Not gadgets operating independently.

A house making decisions as a system.

Don't Automate Everything Just Because You Can

There is always a danger with smart homes.

We can spend £1,000 and consume weeks of our time constructing an elaborate system designed to save £17 a year.

Technology should solve problems rather than create hobbies disguised as energy efficiency.

Although, admittedly, building the system can be quite an enjoyable hobby.

The simplest solution is sometimes still:

close the curtains.

But smart technology becomes worthwhile where it helps us consistently do the right thing without having to remember.

That is where heating automation has succeeded.

Summer automation could do the same.

The Best Smart Home May Sometimes Do Nothing

Perhaps this is the biggest philosophical change.

We tend to judge technology by what it does.

The smartest summer house may frequently decide not to switch something on.

It does not run the fan because the room is empty.

It does not activate the air conditioning because the temperature will fall naturally in an hour.

It does not open the windows because the air outside is hotter.

It does not close every blind because winter sunshine is providing useful warmth.

Good automation is not about making everything happen automatically.

It is about making the right thing happen automatically.

And quite often, the right thing is nothing at all.

A Practical Smart-Summer Experiment

If you already have some smart-home equipment, try this during the next hot period.

For one week, record the highest temperature reached in your warmest room.

Then experiment.

Day 1

Normal behaviour.

Day 2

Close blinds before direct sunlight reaches the room.

Day 3

Keep windows closed while outside temperatures exceed inside temperatures.

Day 4

Ventilate aggressively once evening temperatures fall.

Day 5

Combine shading and night ventilation.

Day 6

Add fans only while rooms are occupied.

Day 7

Combine everything.

You may discover something much more valuable than simply knowing how powerful an air conditioner you need.

You may discover that you can prevent much of the overheating in the first place.

Cooling Is Becoming Part of Home Energy Management

For decades British energy efficiency meant keeping heat inside.

Double glazing.

Loft insulation.

Cavity-wall insulation.

Draught proofing.

Thicker curtains.

Those remain extremely important.

But increasingly our homes face a more complicated problem.

In January we want heat to stay in.

In August we may desperately want heat to stay out.

The answer is not to abandon insulation.

Good insulation can help slow heat transfer in both directions.

Instead, we need homes capable of changing their behaviour with the seasons.

Winter:

capture heat, retain heat, minimise losses.

Summer:

block solar gain, minimise internal heat, ventilate intelligently and cool only when necessary.

That is a much more sophisticated approach to energy efficiency.

Perhaps This Is the Next Smart-Home Revolution

The first generation of smart homes gave us remote controls.

We could turn lights on from our phones.

The second generation gave us automation.

Heating schedules, smart thermostats and occupancy sensors began doing jobs for us.

Perhaps the next generation needs something more interesting.

Judgement.

Not simply:

"The temperature is 26°C, therefore switch on cooling."

But:

"The temperature is 26°C, nobody is home, the western blinds are open, outdoor temperature is 29°C and the sun will set in two hours."

Therefore:

close the blinds and leave the air conditioner alone.

That is genuinely smart.

We have spent years teaching our homes how to keep us warm without wasting energy.

As hotter summers become something more British households have to manage, perhaps it is time to teach them the opposite skill.

Keep the heat out.
Use free cooling when nature provides it.
Cool people rather than empty rooms.
And only consume electricity when there is genuinely something to be gained.

Because the greenest kilowatt-hour is often not the one generated by a solar panel.

It is the one the house realised it didn't need to use at all.