For those living off the grid, or thinking about going solar, the energy to run an HVAC unit is a common concern.
The power requirements of Heat Pumps and Air Conditioners are a big subject. You certainly can run a heat pump on solar. The number of amps required to run a Heat Pump depends on its size and its efficiency.
We can look at a variety of Heat Pump types and discuss the power requirements of each.
- Volts x Amps = Power
- Ductless vs Forced Air Units.
- DC Heat Pumps.
- AC Heat Pumps.
With a little research, you can put together a solar-powered HVAC unit. A little number crunching, some investigating, and a surprisingly small investment can have you on your way to a heat pump system that will not impact your electric bill.
If you are off-grid and thought you could never have air conditioning, that is no longer true. Even better, there are a few DIY systems you can do entirely on your own.
Volts and Amps and Power
Heat pumps require a certain amount of power to operate. They come in a variety of voltages, so calculating the number of amps required can be a little tricky. Luckily, the math to calculate watts, volts, and amps are simple. And, the same equations apply to all basic electrical systems.
The basic power equation is:
- Power(watts) = V(volts) x I(amps)
- In English :Watts is Volts times Amps.
The equation can be manipulated to calculate amps.
- I (amps) = Power(watts) / V(volts)
- In English : Amps is Watts divided by Volts.
If you have a heat pump that is rated at 2500 Watts and is designed to run on 240 volts, the equation to calculate amps would be:
- I (amps) = 2500 watts / 240 volts
- 10.41 amps = 2500 watts / 240 volts
The equation works the same for AC or DC voltage. Remember that an electrical circuit should always be designed to handle twice the required load. In the case of this heat pump, the circuit should be able to handle 20 amps.
Basic Types of Heat Pump Systems
There are two basic types of Heating, Ventilation, Air Conditioning (HVAC) systems commonly used on homes. The older technology is the Central Air or Forced Air system.
The newer technology is known as the Ductless or Mini-Split system. Each system has its advantages and disadvantages.
Central Air System
The outdoor portion of a Central Air Heat Pump system consists of a compressor, a heat exchange coil, and a fan. The fan circulates the air through the heat exchange coil. The coil collects or exhausts heat.
The compressor condenses the heat or cools and pushes it into the house via some form of freon. The freon passes through another heat exchange unit in the duct-work of the house.
A fan in the duct-work blows air through that heat exchange unit. The air takes on the heat or cool from that heat exchange unit and circulates it through the house.
PROS
- Provides a whole house of heating or cooling.
- Less up front investment for unit.
- Duct system enables filtration of air.
- Provides air circulation throughout whole home.
CONS
- Requires duct system, which can be expensive.
- Difficult to heat or cool zones of a home.
- Higher power consumption.
- Ducts require annual inspections and/or cleaning.
A Central Air Heat Pump is well suited to heat and cool large and multi-story homes.
A Central Air system for a 1500 foot home typically requires a minimum of 2500 watts to operate. There are many variables involved in the overall efficiency of an HVAC system.
Ductless Systems
A ductless heat pump system consists of an outdoor unit and an indoor unit. The outdoor unit consists of a heat exchange coil, a fan, and a compressor. The fan blows air through the heat exchange coil.
The coil exhausts or collects heat. The compressor condenses that heat or cool and pushes it into the house via some form of freon. The indoor unit of the ductless system contains a wall-mounted heat exchange coil and a small fan.
The fan blows room air through the coil. The air transfers the heat or cools directly to the room.
PROS
- Provides zone heating and cooling.
- Lower power consumption.
- Larger outdoor unit can heat and cool multiple rooms/zones.
- Closed system improves efficiency.
CONS
- Indoor units may be obtrusive to some homeowners.
- Condensate line from indoor unit must have a place to drain.
- May require multiple systems for larger home.
Ductless Heat Pumps are ideal for small homes, or homes with no existing ductwork.
The ability to control each zone individually makes the systems more energy-friendly. A mini-split designed to cool up to 1000 square feet can draw as little as 800 watts.
AC Power Requirements for Heat Pump Systems
Calculating the power requirements for any HVAC system is fairly simple. Using the Basic Power equation, we can calculate the current in amps required for any size heat pump.
A Large Heat Pump
We will calculate the power requirements of a Central Air Heat Pump system. We will assume a total power rating of 3500 watts. Most large HVAC systems are designed to utilize 240 volt AC power. This is done to keep the current values from getting too high. Using these values we can calculate the current required in amps.
- 3500 Watts / 240 Volts = 14.58 Amps.
A Small Heat Pump
We can also consider a small Mini-Split Heat Pump. There are several small systems on the market that are rated at 1000 watts and require 120 volt AC power.
- 1000 Watts / 120 Volts = 8.33 Amps.
From this simple comparison, it is clear that there is a wide range of power requirements for air conditioning units.
Both are attainable with solar power. The large unit would require ten or twelve 300 watt panels. It would also require a large battery bank and a large 240-volt inverter.
The small unit would only require four 300 watt panels, a small bank of batteries, and an average-sized 120-volt inverter.
DC Power Requirements For Heat Pump System.
There are a few straight DC power mini-split heat pumps on the market. They are 1000 watt units that run on 48 volt DC power. We can use the same power calculation to evaluate the power requirements.
- 1000 Watts / 48 Volts = 20.83 Amps
These all solar units can operate on as few a three 300 watt panels, do not require batteries for daytime operation (although four 12 volt deep cycles are recommended). By adding a few panels and batteries, the system can be expanded to enable 24-hour operation. These units will heat or cool up to about 800 square feet.
Review and Resources
There is a vast array of Heat Pumps on the market. The power requirements of such systems are almost as a variable. With a little research and some simple math, you can calculate the voltage and current demands of such devices.
Sources
Heat Pump Basics
DC Power Heat Pumps
DIY Mini Split System
Power Calculations
