How to save energy in a building on your HVAC systems

Part 2 : How to save up to 70% of your energy costs in your building on your HVAC systems.

The term HVAC is often confusing to electrical professionals. In the building context, HVAC stands for Heating, Ventilation and Air Conditioning (not High Voltage Alternating Current).

In general, HVAC consumes the largest portion of our energy in a building.

The easiest and most cost effective way to slash your energy bill in a modern building is by using variable speed drives to control your ventilation.

Here’s why:

Traditionally ,there are shutters at the air inlets to a building which channel air from the fan to , through the air ducts , into the room. When the user wants more air, they open the duct. When the user wants less air, they close the duct. All the time, the fan motor is spinning at full speed - even though the building is only making use of 50% of the air flow.

Here’s the problem (and the solution)

When a motor spins, the flow of air or liquid is proportional to the shaft speed. BUT, pressure is equal to the square root of shaft speed, and , crucially, energy used is equal to the cube root of shaft speed. That means that at 50% required air flow, we are wasting more than 70% in electricity. 

OK, that’s too much maths. Let’s put that into perspective:

Let’s say that a motor shaft is spinning at 1000 RPM (revolutions per minute) , and is consuming 10 KW of electricity.If the building requires 100% air flow, then that means that the vents will be 100% open, so we will be making full use of the energy input.

BUT, if we only needed 50% of the air, and we closed the vent 50%, then we would have high pressure in the vent (since we closed the valve to 50%), but our motor would still be using 100% of the available energy (10 kw).

Now, if we used a Variable speed drive instead of a standard DOL (Direct Online) approach to operating the motor, our motor shaft would be spinning at 500RPM to achieve 50% air flow. But (here’s the amazing bit) the motor would only be using 2.5KW of energy. That’s amazing!

A variable speed drive installation will typically pay for itself in a matter of months, and go on to repay the entire investment over and over again in its lifetime.

So, to save massive amounts of energy (and the penguins in the north pole), be sure to incorporate variable speed drives in your building design.