A recently published article about the Hybrid HVAC system expounded upon the consumer acceptance of this approach. After all, the auto industry is making sound inroads with sales of their hybrid cars. So, why shouldn’t the HVAC contractor? The article went on to say that a Hybrid HVAC system coupled a heat pump with a gas furnace and provided considerable savings to the homeowner. “Old Timers” recognise this Hybrid as a new name for “Dual Fuel” systems. However, the consumer may now be willing to accept the ‘Hybrid’ term rather than the confusing “Dual Fuel” name. The contractor surely deserves recognition for bringing this concept into the 21st century.
Since the introduction of dual fuel in the HVAC industry as far back as 1974, the concept has been confusing to most consumers and turned many off – when simply promoted as a heat pump first with a fossil fuel back up. The new Hybrid term is readily grasped and accepted by the consumer as not only a fuel savings product but also an environmentally friendly product. So, why not to dress up your sales approach, as well as your profits, and promote this Hybrid product to your customers.
If you’re still doubtful about the comfort level of heat pumps, consider 2 things. First, the heat pump will not be operating at extremely low temp as the fossil fuel heat will be operating and providing the higher leaving air temp that customers may be more comfortable within their homes. Second, with the advent of variable speed products, many heat pumps approach these more acceptable temp even at extremely low outdoor conditions. Variable speed allows for decreased airflow until full demand is required and the higher leaving air temperature can be demonstrated as follows:
Temperature Rise can be expressed as the “Delta T” (the temperature difference between the return air and the leaving air).
Delta T = Btuh divided by 1.08 Times the cfm. So, a three-ton heat pump without variable speed with 36,000-btuh capacity and operating at 1200 cfm would provide a temperature rise of 27.8 and with a return air temperature of 70 degrees would provide a 97.8 leaving air temperature or not much above body temperature. But, with variable speed the airflow might be as low as 960 cfm and the resultant air temperature would be 34.7 degrees and provide a leaving air temperature as high as 104.7 degrees with the same 70-degree return air temperature.
In any event, if you were truly into “Green”, you might ponder the true reduction in particulates with this system. However, just as with the hybrid car, the heat pump will be operating on electricity most of the time and electricity does not contribute to air pollution. Or does it? If the electric plant is operating on fossil fuels for generation, it could be argued that there is no real reduction in particulates to the atmosphere. However, keep in mind that electricity is 100% efficient as there are no waste products going up the flue of the home and most generating plants are government regulated as to the amount of particulates they may put into the atmosphere – and even coal generating plants have greatly reduced their particulate output. So, there is every reason to accept the idea that this hybrid HVAC system is more environmentally friendly. In any event, that argument is up to the EPA (Environmental Protection Agency), and does it really matter how “Green” the concept is as long as the consumer is willing to accept the idea?
What about the fuel savings aspect of the hybrid system? Electricity costs more per btuh than fossil fuel, or does it. Everyone knows that the new gas furnaces are 80to 90% efficient, but did you consider that a heat pump is 300% efficient? That is right because electricity is 100% efficient (no products of combustion going up the chimney), and the typical heat pump has a coefficient of performance of 3.0 or better and that is 300%! Simply put, for every 1 dollar of electricity used to operate the heat pump, you get 3 dollars of usable heat. So how much could a consumer expect to save?
Using the ENERGY STAR HVAC formula from the EPA website for comparisons with the following assumptions yield some interesting figures. We’ll compare an existing 80% AFUE furnace and a 10 SEER AC to a new 80% AFUE furnace with variable speed, night set back stat and a 13 SEER Heat Pump in the Mid Atlantic.
Assumptions
- 36,000 btuh Heat Gain
- 60,000 btuh Heat Loss
- Natural Gas per therm @ $1.15 (probably a low figure)
- Electricity .095/kW summer and .085/kW winter
- 2250 hours of heating & 1000 hours of cooling
- 75% of heating hours by the heat pump*
- 25% of heating hours by the furnace
*Typical winter average temp. in the Mid Atlantic region is > 30 deg 80% of the time, and the balance point in this example would be @ 30 degrees. However, some defrost will occur, thus we might safely assume 75% of the heating hours would be by the heat pump.
So, a typical three ton system with natural gas in the Mid Atlantic area could save as much as $1000 a year ($2282 – $1282)! Assuming that our example demonstrates the typical heating and cooling bills to be about $2282 annually in the region, this would be a realised savings of about 40%. Additionally, if you’re really into being “Green”, the website said that the environmental impact would be like planting some 500 trees or not driving some 95,000 miles.
The Integrated System
If “Dual Fuel” can be dressed up under the name of a “Hybrid HVAC” system and readily accepted by the consumer then why not an integrated system as well! Just for those who came in late, an integrated system uses the standby heat (heat normally wasted up the flue) from the domestic water heater. This system eliminates the gas furnace and uses a hot water coil. The savings here could be another 10 to 20%. This could cut the Homeowner’s utility bills by 60% or more and have an equal or greater impact on the environment.
Essentially the integrated system was promoted in the late 1970’s and early 1980’s and was commonly known as the “Appollo” system. The system was primarily used for multi-family projects (apartments), as the heat loss was usually less than 30,000 btuh. This being the case, it made sense to use the domestic hot water heater with a pump and coil to provide the heat and straight air conditioning for cooling. I’m not sure if that much thought was initially given to the energy savings as was the cost. After all, why have a 50,000-btuh-gas furnace with a 40,000-btuh output when there was going to be a hot water heater right next to it with about 35,000 to 47,500 btuhs available. Remember that during these early stages, these hot water heaters were vented by B-vent. Today, we have direct vent hot water heaters that greatly reduce the amount of heat being wasted up an open vent.
In either case, there does exist an energy savings as the water heater is constantly maintaining 125-degree domestic water temperature and is only used sporadically. Keep in mind that there may be considerable loss up the flue _ when the domestic water was not being used and even some with a direct vent water heater.
So, the integrated system would be using some of this wasted heat to provide space heating. Additionally, Appollo recommended increasing the water heater size to reduce complaints of lack of hot water when demanded for domestic use. Thus the entire heat loss could easily be off set when space-heating demand was required.
The use of a heat pump instead of the straight AC with the Appollo concept was introduced in California by “CALERDA”, an energy-regulating program, which eliminated, by law, the use of any electric resistance heat in multi-family applications. So, it made perfect sense to use this concept. Many multi-family units used such systems in California, and probably still do so. The point is, this is really nothing new. However, let us consider the actual operation and make some estimates of possible energy savings.
The heat pump portion of the integrated system functions exactly as any straight heat pump. It is in the “back up” heat operation that the integrated system begins to make a considerable difference. Back up heat is required during two separate operations. First, during a defrost cycle some additional heat is required even though the typical defrost cycle is usually only 3 to 5 minutes. Without some additional heat there would be a “cold blow” throughout the home and this would result in discomfort and homeowner complaints. Second, when the outdoor temp drops below the balance point (the temp at which the capacity of the heat pump can no longer maintain set point temp in the home) the back up heat will be required, same as “Dual Fuel”.
The domestic hot water heater with the integrated system handles both of the above requirements. The amount of heat needed to off set the defrost cycle is very minimal – and because the duration is so short it may never require the water heater to initiate operation. The heat required once the heat pump is no longer capable of supplying adequate heat (commonly called second stage operation) will take advantage of the stand-by heat of the water heater as well and it will require a considerable operating cycle before the water heater will actually begin to heat the water. This is when true savings come into play, as there will be no resistance heater operation (the most costly part of heating with a heat pump).
Additionally, the hot water coil will provide water temp of at least 125 degrees and when added to the heat out put of the heat pump during 2nd stage demand, the leaving air temp may typically be in excess of 125 degrees. More importantly, this will not only tend to shorten the second stage heat operation as the mass of the hot water coil will provide higher leaving air temperatures even after termination. This means far greater comfort levels.
Okay! This is all fine as long as there is a low heat requirement as in a multi-family application. Yes, but the principle works equally well in single-family home applications. Consider that the typical system in the mid Atlantic is a three-ton heat pump with a fifteen kW back up resistance heater. Well 15 KW is about 50,000 btuh (15 X 3413 = 51595 btuh). So, the hot water heater needs only to provide about 50,000 btuh and most 50-gallon water heaters (gas or oil) will meet this requirement. Admittedly, a home with two heat pump systems might require two water heaters or a larger water heater, which might not be a bad thing. However, the principle remains sound.
So what products would actually be needed? Obviously a properly sized heat pump and duct distribution system would be required. A water heater with the capacity needed for back up heat, and again some consideration for domestic hot water needs. This is not a big thing – as most water heater manufacturers have manufactured double walled hot water heaters for this application for some years – and even have separate inlet and outlet connections for the hot water coil. A hot water coil with the required heating capacity and a matching pump assembly (usually a three gpm Grundfos or Taco pump) to supply the coil would also be needed. What would not be needed is another number 8 wire and 60-amp breaker as there would be no resistance heater.
I would also recommend a “Hot Water Re-claim” unit be installed. These products take advantage of the waste heat from the compressor and heat the domestic water – and remember we’re using the domestic water heater for space heat. During the summer season the re-claim unit might easily supply all or certainly most of the heat required for domestic hot water usage.
There is some concern that the re-claim unit, when operating in the heat mode, might reduce the heating capacity of the heat pump at extremely low temp. However, what does it matter if we are using the water tank for back up heat when required? Heat is heat and does it really matter where it comes from! Additionally, the re-claim unit raises the SEER during the cooling season. This is true as normally an outdoor unit is working with refrigerant temp approaching 300 degrees but the reclaim unit portion is only working against 125-degree water temp in the hot water heater. You shouldn’t be surprised if the amp draw is reduced by 30 or 40% or increasing the SEER by two or three points over the cooling season.
So, what might we expect for savings on the overall utility bill. How about 40 to 50% in heating and another 20% in cooling! Keep in mind that no comparisons are available today, so I must go by the savings I have experienced with this system in my own home over the past 20 years. I’ve operated this system consistently and currently spend about $1200 annually for heating and cooling 2880 square feet of living space. Further, my back up source is LP Gas at over $2.95 per gallon. Neighbors with similar homes in my area spend over $3,000 annually for their heating and cooling bills, so I save 60% annually.
So, dress up your sales presentation with the new HYBRID HVAC System and increase your profits as well! And don’t forget about the “Integrated Systems” for your next project.
