Heat Pumps use the outside air to heat a home in winter and cool it in the summer. Sounds pretty simple, but, it is a complex, technologically advanced system. Two trends are helping to make heat pump systems and rooftop solar cost effective and even less expensive to operate, especially when the two systems are combined.
The cost of the components in a rooftop solar system have come down dramatically the past few years and rooftop solar systems have become so efficient and cost effective they now generate electricity inexpensively, often for much less than what you would pay your local utility. And, there is a new generation of smaller, variable speed heat pumps called “ductless mini-split systems” that allow you to heat and cool a few rooms at a time instead of your entire house, including rooms that are seldom used. The combination of inexpensive solar electricity and a “zoned” approach to heating and cooling are often less expensive than natural gas heat and central air conditioning.
Staging or modulating or variable speed refers to a Heat Pump’s ability to run at less than its maximum capacity…this allows it to increase comfort levels and boost efficiency. Traditional systems and many of the systems still being installed today are single-stage. Having a two-stage or multi-stage system nearly eliminates temperature fluctuations. Your system glides along barely sipping electricity.
It runs at lower speeds for longer periods of time offering:
- Advanced temperature control
- Lower humidity
- Reduced sound
- Enhanced filtration
- Lower cost to operate
How do Heat Pumps Work?
Heat Pumps are best for moderate climates, like ours. Heat pump systems deliver tremendous comfort year round and they are extremely energy efficient.
A Heat Pump operates as a heat transporter. It is constantly moving warm air from one place to another, to where it’s needed or not needed, depending on the season. Even in air that seems cold, heat energy is present. When it’s cold outside a heat pump extracts the heat present in the outside air and transfers it to the inside. When it’s warm outside it reverses direction and acts like an air conditioner removing warm air from your home.
Heat pumps exploit the physical properties of a volatile evaporating and condensing fluid known as a refrigerant. The heat pump compresses the refrigerant to make it hotter on the side to be warmed, and releases the pressure at the side where heat is absorbed.
The working fluid, in its gaseous state, is pressurized and circulated through the system by a compressor. On the discharge side of the compressor, the now hot and highly pressurized vapor is cooled in a heat exchanger, called a condenser, until it condenses into a high pressure, moderate temperature liquid. The condensed refrigerant then passes through a pressure-lowering device also called a metering device. This may be an expansion valve, capillary tube, or possibly a work-extracting device such as a turbine. The low-pressure liquid refrigerant then enters another heat exchanger, the evaporator, in which the fluid absorbs heat and boils. The refrigerant then returns to the compressor and the cycle is repeated.
It is essential that the refrigerant reach a sufficiently high temperature, when compressed, to release heat through the "hot" heat exchanger (the condenser). Similarly, the fluid must reach a sufficiently low temperature when allowed to expand, or else heat cannot flow from the ambient cold region into the fluid in the cold heat exchanger (the evaporator). In particular, the pressure difference must be great enough for the fluid to condense at the hot side and still evaporate in the lower pressure region at the cold side. The greater the temperature difference, the greater the required pressure difference, and consequently the more energy needed to compress the fluid. Thus, as with all heat pumps, the coefficient of performance (amount of thermal energy moved per unit of input work required) decreases with increasing temperature difference.
How Do I Know Which System is Best for Me?
Many factors can influence the savings on your energy consumption, including lifestyle, the efficiency rating of your equipment and having the right-sized system for your home. Properly sized, higher efficiency systems provide improved comfort at reduced operating costs by using fewer energy resources.
Another vital step to having the most energy efficient system is to have Alternative HVAC Solutions conduct a load calculation. Most homes today are heated and cooled by units that are too big for the home – others are too small. When an air conditioner or heat pump system is not the proper size an array of problems can result. Temperatures might be uneven. Units might not run long enough to properly control humidity. You may even have more maintenance problems over time. And, the money you think you are saving may be reduced because with units that are oversized, you’re essentially paying to heat or cool space that isn’t there.
Programs and Rebates
There are many rebate programs promoting energy efficiency. Here are three prominent examples:
City of Palo Alto Residential Efficiency Rebate Programs:
Bay Area Air Quality Management District