Saving electricity in rental units: start with air conditioning

High electricity bills are a common complaint among homestay and serviced apartment owners. The notable point: most of the wasted power is not used while guests are using the unit, but when nobody is inside.

Sold rooms are often empty

A field study by the Western Cooling Efficiency Center at the University of California, Davis (USA) monitored hotel rooms throughout summer 2010. The results:

• Rooms were sold on about 77 - 79% of days.
• But people were actually in the room only about 56 - 57% of the time.

In other words, for almost half the time a room with a guest had nobody in it. Guests go out to eat, sightsee or work, and the air conditioner often keeps running.

For the same group of rooms, controlling air conditioning by occupancy saved about 25% of cooling energy. The study was carried out in a mild coastal climate on a small number of rooms. In Vietnam, air conditioners run more hours per year, but the actual figure should still be measured on your own units.

Three common sources of waste

1. Guests go out and leave the air conditioner and lights on. This is the largest item and it repeats every day.
2. Units sit empty between two stays. The cleaner turns on the air conditioner while working and forgets to turn it off, or the owner switches it on in the morning for a guest arriving in the afternoon.
3. Machines failing quietly. An air conditioner with a dirty filter or low refrigerant runs longer without cooling better. Nobody notices until a guest complains.

What to do, in order of priority

1. Cut load when the unit is empty

Use presence sensors, or door status combined with the booking calendar, to know that nobody is in the unit. After a delay (for example 15 - 30 minutes, as the owner sets), turn off the air conditioner and lights automatically, and keep the refrigerator and sockets that must run continuously.

2. Pre-cool before guests arrive, do not run all day

Instead of switching the air conditioner on in the morning, set a scene that turns it on about 30 minutes before check-in time. The unit is cool when the guest walks in, and the machine does not run for hours with nobody there.

3. Track power per unit

With daily power figures for each unit, comparing units of the same type shows at once which one consumes abnormally. A unit that uses far more power at the same occupancy rate usually needs its air conditioner cleaned or repaired.

4. Set sensible limits and tell guests

Set a minimum allowed temperature (for example not below 20 degrees C) and state it in the check-in instructions. Guests who understand the reason complain less.

What TingStay does

• Knows whether a unit is occupied, from presence sensors (Brand Kit) or from door status and the booking calendar.
• Scheduled scenes: pre-cool before check-in, cut load after check-out or when the unit is empty. Scenes run on the TingEdge in the unit and keep working when the internet is down.
• Wall-mounted air conditioners are controlled through an infrared transmitter with current sensing, so the system knows whether the machine is really on or off.
• Power consumption per unit, comparable across units.

To estimate savings and payback for your own setup, use the calculator on the In-unit hardware page.