SPACE HEATING & COOLING: Other Types of Heating

Questions:

• Will a heat pump cost less than a gas furnace to provide the same amount of heat?
  
• Are heat pumps, when operating as an air conditioner, more efficient than conventional air conditioners?
  
• What is a ground-source heat pump?
  
• What would cause the radiators on the first floor to get hot while the second floor radiators stay cool on my hydronic (hot water) heating system?
  

Will a heat pump cost less than a gas furnace to provide the same amount of heat?
The two units are receiving their energy in different forms.

Heat pumps operate on electricity, and gas furnaces consume natural gas. Differences in fuel prices and differing efficiencies both affect the cost of delivering heat.

At current natural gas prices of about $9 per 1,000 cubic feet, a dollar's worth of natural gas can produce about 200,000 British thermal units (Btu), that is, if extracting all available energy. If a furnace is operating at 80 percent efficiency, it delivers about 140,000 Btu for each dollar spent on fuel. A high-efficiency furnace might deliver 190,000 Btu for each dollar spent.

A typical heat pump delivers about twice as much energy as it consumes. Average residential electric prices are about 7 cents per kilowatt-hour. Often electric utility companies offer lower electric rates for all electric homes. Using an electric rate of 4 cents per kilowatt-hour, a dollar will buy about 170,000 Btu. If prices are 7 cents per kilowatt-hour, the heat delivered is reduced to 97,500 Btu per dollar spent

Both energy prices and equipment performance together determine the cost of delivering heat to home.

Are heat pumps, when operating as an air conditioner, more efficient than conventional air conditioners?
The efficiency of a heat pump during the cooling season is not necessarily greater than the efficiency of an air conditioner.

Both air conditioners and heat pumps are rated according to their seasonal energy-efficiency ratio (SEER). This rating represents the seasonal cooling efficiency rather than a peak efficiency. According to the Air Conditioning and Refrigeration Institute (ARI) directory, air conditioners are available with higher SEER ratings than heat pumps.

The cost of purchasing a heat pump is usually higher than an air conditioner of the same size. The additional cost of the heat pump may be better spent by purchasing a higher efficiency air conditioner, if the primary purpose of the heat pump will be for cooling.

What is a ground-source heat pump?
A ground-source heat pump is a heating system that uses the earth as a heat source in the wintertime, and as a heat sink to eject the heat in the summertime.

Ground-source heat pumps may be either open-loop or closed-loop.
A closed-loop system circulates the same water through the loop for the heat source and heat rejection process.

The closed-loop heat source or sink may be a vertical hole or horizontal trench.
The advantage of the closed-loop system is that the water in the loop, because it is recirculating, can be treated, and the system can be used in areas where the water in the water may be contaminated or hard.

An open-loop system would be used where the water quality is good and with soft water. The advantage of the open-loop system is the initial cost is usually lower, and the efficiency is usually higher.

What would cause the radiators on the first floor to get hot while the second floor radiators stay cool on my hydronic (hot water) heating system?
Hydronic heating systems can get air trapped at the highest locations in the system. Water systems may have automatic air-bleed valves at the highest point of the distribution system to purge the system of air. If there are no bleed valves, the velocity of the water is designed to remove the air.

In some cases, radiators located higher than the distribution system may have bleed valves. Check these valves. If they are operated manually, they may need to be bled as problems arise.

Another problem may be the loss of water in the system. This is typically caused by an automatic water makeup valve, or pressure-reducing valve stuck in the closed position. This will decrease the pressure of the system, and it could cause air leakage into the system. Air leakage will increase the potential for air locking.

Unless a person has technical training in these systems, contact the heating service personnel to determine the source of the problem.