Upgrading My Heat Pump and Ducts

Though I had always assumed that when the time came I would replace my heat pump with a geothermal heat pump, that’s not what happened. I am replacing my air heat pump with another air heat pump, a more efficient one, and re-ducting the attic to create a more efficient and effective system. The cost to reconfigure my finished basement ($5,000-$10,000) and install either a vertical coil or standing column well ($12,000-$18,000) combined with technical difficulties, limited cost savings and the potential I might impact the drinking water aquifer or damage my garden ended my plans to retrofit a geothermal unit into my existing home.

Lots of things have changed since this house was built in 2004 (with builder grade system). First of all an air heat pump is usually a split heat-pump systems consisting of two parts: an indoor (coil) unit and an outdoor (condensing) unit. Both units are designed to work together.  Heat-pump systems manufactured today, by law, must have a seasonal energy efficiency ratio (SEER) of 13 or higher while my heat pump has a SEER of 12 and a HSPF less than 8. Seasonal Energy Efficiency Rating (SEER) or Heating Seasonal Performance Factor (HSPF) for heat pump systems are the efficiency ratings on heat pumps, the higher the SEER/HSPF, the more efficient the equipment. The SEER is measured in average Btu output over the season divided by the watt hours and is the standard measure of energy use efficiency. The Air Conditioning, Heating and Refrigeration Institute (AHRI), defines the method to measure SEER. AHRI was formed in 2008 by a merger of the American Refrigerant Institute and the Gas Appliance Manufacturers Association. Generally, the higher the SEER/HSPF of a unit, the higher the initial cost and lower the operating cost. For these new, high-efficiency systems to work properly, the outdoor unit and indoor unit must be perfectly matched, properly sized and correctly ducted to deliver the right air flow.

New Energy Star certified air heat pumps have minimum requirements of a 14.5 SEER, 8.2 HSPF and 12 EER or higher. Air heat pumps are available with Up to 20.5 SEER; and Up to 13 HSPF. Two-stage or variable cooling makes this possible.  The heat pump has a compressor with two or more levels of operation: high for hot summer days and low for milder days. Since the low settings are adequate to meet household-cooling demands on all but the hottest days, a multi-stage unit runs for longer periods and produces more even temperatures. Longer cooling run cycles allows a two-stage or multi stage heat pump to remove more moisture from the air and allows you to size the unit for the hottest day capacity without reducing efficiency. The indoor air handler (the fan) provides the energy to move air through the ductwork to the rooms of your house. The high efficiency units also have a variable speed motor that automatically changes speed based on air flow requirements to maintain temperature settings to eliminate the on/off cycling of the blower.

To properly size a system for a home there is Manual J from the Air Conditioning Contractors of America, ACCA. In truth what there really is are several computer models and an iPhone app available that does the calculations for you. The only problems is the input factors that impact the calculation include the climate; the size, shape and orientation of the house; the home's air leakage rate; the amount of insulation installed; the window areas, window orientations, and glazing specifications; the type of lighting and major home appliances; and the number of the occupants. Slight variations in the input assumptions get different results. In the model I played with, baseline inputs were available based on square footage, orientation, age of home and zip code and then adjustments could be made. The results were no better than my back of the envelope calculation, but I know my house, the square footage, orientation, the additional insulation and window films I installed and I figure that the heat pumps should be around 3.675 ton.  My existing heat pump turns out to be 3.5 ton.  Once the temperature reached 90 degrees in Virginia the heat pump ran continuously and could not keep the master bedroom or the bonus room cool and is probably one of the reasons why I am replacing an 8 year old system. The high efficiency two-stage or multiple stage heat pump allows me to oversize the unit slightly so that it can handle the hottest days without sacrificing optimal performance on more temperate days so the old rule that if a system is over sized, the system will cycle on and off too frequently, greatly reducing its ability to control humidity and its efficiency is no longer strictly true. If you are going with a multiple stage system round up.

An essential element to the efficient and effective heating and cooling of your home is the duct system, and there is the Manual D by ACCA intended to ensure a good design.  Many homes built after 2000 have flexible ducting and this could be a problem in the performance of your system. ASHRAE, founded in 1894, is the leader in research focused on building systems, energy efficiency, indoor air quality and sustainability.  ASHRAE sponsors research a various universities to advance the sciences of heating, ventilating, air conditioning and sponsored a series of studies between 2002 and 2006 that found that the airflow loss in flexible ducting in real world installations was 9-10 times the loss anticipated in the 1999 design standard used in Manual D in most homes built during the last building boom. In addition, the experimental results they also found that with compression ratios exceeding 4% (the minimum compression found in the real world), the duct performance varies considerably with slight variations in the installation. A low skilled, inexperienced or sloppy worker does a poor job that will impact the performance of your system.  

The ducts in my well insulated attic

An examination of my ducts in the attic found a poorly executed installation. I should not be surprised since several of the ducts were not properly attached to the distribution boxes when we first bought the home from the lender. I had the ducts sealed when I added additional insulation to the home. The flexible ducts in my attic are R-6 with a black vapor barrier. The flexible ducts consist of three layers an inner core of a metal helix encased in a plastic or foil film, and insulation layer and the outer vapor barrier jacket. While fully extended properly installed flexible duct can be as good at maintaining air pressure as a galvanized steel duct, performance deteriorates as the ducts sag. In all the real world tests there was some degree of compression or sag (more than anticipated) even in good installations. In poor installations there were sharp bends, excess lengths and significant restrictions due to squishing the duct into tight spaces. When the flexible ducts are compressed (or sagging) the inner layer crumples (it is a soft spring) and the helix pops out. Instead of smooth circular tube the flexible duct turns into a bumpy pathway for the air that causes turbulent flow and very significant pressure drop from the beginning to the end of the duct. In my case, almost no air flow in the bonus room.  The scientists at Berkeley Livermore Laboratory and Texas A & M found this effect to be orders of magnitude above the range provided in the ASHRAE design standards. The reason the drop was so great is that the ducts operate at very low pressure and small resistance due to fitting or duct friction can have a very big impact on flow. The scientists calculated pressure drop correction equations so that systems designer could correct for this effect.  

I did not even bother to look for a Manual D computer program. The solution to improving my duct air flow was simply to install galvanized steel trunk lines and distribution boxes, properly sealed with UL 181 foil-backed butyl tape and with R-8 (or higher) reflective insulation. The trunk lines will have straight runs and gentle curves to the distribution boxes, but I am going to use flexible R-8 to tie into the last foot of the vent sleeves (to avoid replacing all the boots) keeping the transition as smooth as possible. I am going to use reflective insulation at a minimum of R-8 to take advantage of what little boost I can get from the decreasing the emittance of the ducts. Radiant barriers on your ducts work in your attic to prevent some of the heat from the roof from being transferred into the ducts. The idea is to have the radiant barrier or coating reflect some of the heat of the attic space away from the ducts. Oak Ridge National Laboratory, ORNL, found in field experiments that radiant barriers installed in the attic could reduce air conditioning bills in the hottest parts of the country, so hopefully I will get some small boost from it. In addition, I will install a temperature controlled attic fan to reduce peak temperatures in the attic, but allow the attic to benefit from southern exposure heat gain in the winter. The new insulated and sealed galvanized ducts and new properly installed reflective flexible duct supply lines to existing registers will add several thousand dollars to the cost, but should significantly improve performance of the system and the galvanized steel portion of the ducts will last for decades. Total cost $16,400. After the work is done I will have to blow more cellulose into the attic to correct what has settled or was disturbed in the installation.

Carbon Footprint, Carbon Savings and Carbon Offsets

All resources are finite. As humans our resources consist of money, time, passion and energy. In the end, where, how and when we deploy these resources will determine our comfort and happiness with our lives. While there are some basic truths, the optimal allocation of your resources is based on your values and goals. We all should be thoughtful in our living, smarter about the ways in which we use the earths and our personal resources.

According to McKinsey and Co. it cost an additional $30-$40 above normal energy production costs to eliminate one ton of CO2 emissions by replacing traditional energy production with solar or wind power (the presumed life of the equipment was unreported). However, when a ton of CO2 was saved using LED light bulbs or energy-efficient appliances money was also saved ($108-$159 less was spent on energy for every ton of CO2 saved). The costs associated with generating power without CO2 emissions are higher than current costs. If the money is spent to reduce CO2 by replacing generating capacity there will be less money to spend on other things that matter to you or are necessary for your life, but if you reduce the use of energy less money is spent on energy and more money is available for other goals.

When you use less energy, by insulating, changing to lower energy light bulbs, controlling passive solar heat, or using energy star appliance, less energy is used, less CO2 released and money is saved. Reducing your energy consumption is a far better utilization of resources. While solar panels and wind turbines are sexy, and renewable sources of energy sound wonderful, these technologies are still in their infancy. Geothermal generation of heating and cooling and nuclear generation of power have failed to catch on in the United States, but have advanced significantly in the past few decades in overseas locations. Conservation and energy efficiency are currently well developed technologies, effective and relatively cheaper. Use less so that we can all live within the productive capacity of the existing infrastructure. Then only expand the generating capacity in ways that do not release CO2, do not burden the earth.

Adding insulation and sealing existing homes and commercial buildings is by far the low hanging fruit and a good source of “green economy” jobs. The Wall Street Journal reports that heating and cooling buildings account for about half of the CO2 emissions in the U.S. My home was built in 2004 and is heated and cooled with a duel system; the upstairs with an air heat pump and the lower levels with a gas furnace and air conditioner. Replacing the heating and cooling systems with geothermal systems would only make sense when the existing systems reach the end of their functional life. After eliminating incandescent light bulbs, upgrading all appliances to energy star, installing reflective films on the window and installing drapery, I found that adding insulation was a good way to further reduce the energy consumption of the house. Following the recommendations of the Building Envelope Research of the Oak Ridge National Laboratory the attic, crawl spaces, eves, duct work, underside of a large portion of the main level floor were insulated with cellulose. The pipes, end caps, knee wall, sump pumps and all identified areas were sealed, the garage was insulated and an insulated garage door installed. After six months electricity usage (as measured in kilowatts for the same six months the previous year) had been reduced by over 6% (despite relocating our workspace to the home with all its attendant equipment) and the winter liquid propane usage (as measured in volume use December through March both years) was reduced by 25%. Also, the overall comfort in the bedroom over the garage and the master bedroom has been vastly improved. I was very surprised (and pleased) at the energy savings for what was a well insulated home.

Though I do not need to commute to a job, I still drive my (gas hybrid car) almost 4,000 miles a year. The hybrid does not make economic sense especially because I drive so little. However, it does make me happy to drive so to me it was worth the extra money I paid for it. In searching for the carbon emitted per vehicle mile I could only find the 1993 data from the Nowak study which lists 0.88-1.06 lbs CO2 per mile. This is probably high for my hybrid, which was not available at the time of the study. The same article states that each person in the US generates 2.3 tons of CO2 each year, which appears in conflict with the automobile numbers until you realize that babies and children do not have cars and city dwellers automobile ownership and use is also much less than suburban use. During the eight years I lived and owned a car in the city, I drove less than 1,000 miles a year. After reducing the energy use in my home, eliminating commuting from our lives, reducing frivolous travel I still wanted to do more.

I found the following fact: “A single mature tree can absorb carbon dioxide at a rate of 48 lbs/ year and release enough oxygen back into the atmosphere to support 2 human beings.” The Tree Folks are the source of the above information, and are willing to sell carbon off-sets in the form of trees. I tend to think of carbon off-sets for people who want to vacation in Bora Bora or have the wedding or Oscar party of the century, but in truth they are probably for people like me who use various technologies to make their lives richer and happier. My large house comes with a big piece of land. Admittedly, most of the land is wooded undisturbed land and part of the Chesapeake Bay water shed, but I do have about 3 acres of mostly open land around the house. We planted 43 trees of moderate maturity (over 6 foot each). Using the Tree Folk data, forty-two trees absorb a ton of carbon a year and the last tree replaces a diseased tree we cut down. Beyond watering the trees in the first three weeks they were planted, they have thrived on benign neglect. I am already drawing up plans, researching native trees, and saving my nickels for another 3.6 tons of annual carbon off-sets otherwise know as another 150 trees. I may have to make that 152 trees because there are two more existing trees that are not doing well.

Trees can also reduce air conditioning and heating needs by providing shade and providing a wind shield for winter. Trees also act as natural pollution filters. Their canopies, trunks, roots, and associated soil and other natural elements of the landscape filter polluted particulate matter out of the flow towards the water shed and use nitrogen, phosphorus and potassium which are contributing factors to the decay of the Chesapeake Bay water shed. Trees are pretty.