We have been having some cold mornings. There has been frost on the roofs, cars, and plants. We have been getting a lot of calls from people saying that their heat pump is blowing cold air instead of heat. Let me explain why that is and why it is not a problem with your system. If the weather is cold, usually 40 degrees or less, a heat pump will go into what is called "defrost mode." During this time, yes, the air coming out of the vents will feel cool, but this should only last a short time. The temperature in your house may even go down a degree or two. Your heat pump is designed to do this in order to give you maximum efficiency (max efficiency = lower electric bills).  If your heat pump never blows warm air or does not get up to temperature, then you might have a problem and should give us a call.

I took this from the International Association of Certified Home Inspectors' website for further explanation of this process.

An excerpt from: “Defrost Cycle of a Heat Pump” - by Ben Gromicko and Nick Gromicko
https://www.nachi.org/defrost-cycle-heat-pump.htm
 
When a heat pump is operating in the heating mode or heat cycle, the outdoor air is relatively cool and the outdoor coil acts as an evaporator.  Under certain conditions of temperature and relative humidity, frost might form on the surface of the outdoor coil.  The layer of frost will interfere with the operation of the heat pump by making the pump work harder and, therefore, inefficiently.  The frost must be removed.  A heat pump has a cycle called a defrost cycle, which removes the frost from the outdoor coil.
 
A heat pump unit will defrost regularly when frost conditions occur.  The defrost cycle should be long enough to melt the ice, and short enough to be energy-efficient.
 
In the defrost cycle, the heat pump is automatically operated in reverse, for a moment, in the cooling cycle.  This action temporarily warms up the outdoor coil and melts the frost from the coil.  In this defrost cycle, the outdoor fan is prevented from turning on when the heat pump switches over, and the temperature rise of the outdoor coil is accelerated and increased.
 
The heat pump will operate in the defrost cycle until the outdoor coil temperature reaches around 57° F.  The time it takes to melt and remove accumulated frost from an outdoor coil will vary, depending on the amount of frost and the internal timing device of the system.
   
When the outdoor coil temperature drops to around 32° F, the thermostat closes the circuit and makes the system respond.  This causes an internal timer to start.  Many heat pumps have a generic timer that energizes the defrost relays at certain intervals of time. Some generic timers will energize the defrost cycle every 30, 60 and 90 minutes.
 
The defrost relays turn on the compressor, switch the reversing valve of the heat pump, turn on the interior electric heating element, and stop the fan at the outdoor coil from spinning.  The unit is now in the defrost cycle.
 
The unit remains in the defrost cycle (or cooling cycle) until the thermostat on the bottom of the outdoor coil senses that the outdoor coil temperature has reached about 57° F. At that temperature, the outdoor coil should be free of frost.  The frost thermostat opens the circuit, stops the timer, then the defrost cycle stops, the internal heater turns off, the valve reverses, and the unit returns to the heating cycle. A typical defrost cycle might run from 30 seconds to a few minutes.  The defrost cycles should repeat regularly at timed intervals.
 
In summary, certain conditions can force a heat pump into a defrost cycle (or cooling cycle) where the fan in the outdoor coil is stopped, the indoor fan is stopped or electric heat is turned on, the frost melts and is removed from the outdoor coils.  When the frost thermostat is satisfied or a certain pre-set time period elapses, the outdoor fan comes back on, and the heat pump goes back into the heating cycle.

It has been a few months since my last post. We are still seeing savings on our electric bill.

After we installed our Mitsubishi, ductless mini-split, we were using it exclusively to cool our house. The unit we installed is a 2-ton, single head. It really is not designed to cool an entire house, but we wanted to see what it could do. We were seeing over 30% savings on our electric bill during the spring. As summer kicked in, our savings dipped a little bit but never got below 20% savings.

Because the system is a single-head, it is not designed to cool the entire house; so if doors were closed, those rooms would get hot. A multi-head system would take care of this problem. 

Since the beginning of August, we have turned on our central A/C system, and the mini-split is being used as a supplement. We just got our latest electric bill, and we are still seeing substantial savings. This latest bill is for $164.77. Last year it was $217.10. That is a savings of $52.33 or 24.1%.

So over the last 7 months we have saved $374.29! That averages out to 27.4%.

The heat and humidity in Florida makes our air conditioners pretty much a necessity, but how exactly do they work? Air conditioners work the same way as refrigerators. They just cool a much larger space. A heater is pretty easy to understand because heat is fairly easy to generate, but how does one create cold? An air conditioner doesn't really generate cold; it uses a chemical, usually Freon, to transfer heat from the indoor air to the outside. Freon is used because it easily converts from a gas to a liquid and back.

An air conditioner has three main parts, a compressor, a condenser, and an evaporator. The compressor and the condenser are usually located outside, and the evaporator is located inside. The Freon arrives at the compressor as a cool, low-pressure gas. The compressor compresses, or squeezes, the gas turning it into a hot, high-pressure gas. This gas then flows to the condenser.

The condenser is the part that has metal fins all around. These fins help the heat dissipate quickly, and a fan blows it away. When the Freon leaves the condenser, it is much cooler and has changed from a gas to a liquid.

The liquid Freon enters the evaporator through a very tiny hole. This causes the Freon's pressure to drop, and it begins to change into a gas and evaporate taking heat from the air around it. By the time the Freon leaves the evaporator, it is, once again, a cool, low-pressure gas ready to start the trip again.

The evaporator also has metal fins and a fan. The fan blows the inside air across the fins, and the heat is removed from the air. The air is much cooler and is then blown throughout the house via the duct work. 

This process repeats again and again until the desired temperature is reached.