A Deeper Look into My Deep Energy Retrofit
My wife and I live in a Title 24 house built in 2004 in Stockton, California. It is a 1,883 ft2 ranch, slab-on-grade, with 9-foot ceilings, double-pane low-e vinyl -framed horizontal slider windows, installed R-30 ceiling insulation (effective R-22), and R-13, 2 x 4 walls with stucco exterior and a tile hip roof. The HVAC system is a 2½-ton, 14-SEER, R-22 unit matched with an 80,000 Btu input 80% induced-draft natural gas-fired horizontal furnace, with a 4-ton blower running at low speed through a 4-ton evaporator coil with an external static pressure of 0.48 inches water column (IWC) delivering 1,275 CFM. The house has a heat recovery ventilator (HRV) moving 105 CFM on high speed. The HRV is designed to bring fresh air into the house and exhaust stale air to create good indoor air quality. Our natural-gas and electric combined utility bills average $145 per month. The blower door readings were 1,875 CFM50, right at ASHRAE 62.2 for minimum ventilation requirements. The duct test was 107 CFM25, with about 8.4% duct leakage.
In the beginning, I remember thinking, Why should I do anything to upgrade my house? It’s good enough—certainly better than most.
I am privileged to be on the staff of an energy training center for a major utility in Stockton, California. We preach envelope air sealing, properly installed insulation, and properly sized and commissioned HVAC systems with sealed ducts that deliver the correct amount of air to each room with the shortest duct runs possible.
My house had none of this. It was time for me to walk the walk and do a deep energy reduction to my house so that I could talk from experience to back up the science that we support. Here’s my story.
A Step-by-Step Process
This project was started in June 2012 and completed in September 2012. The first thing that I did was perform ACCA Manual J heat loss/heat gain calculations. I also performed an ACCA Manual D duct design, using Wrightsoft software, on the building. I sent the results to Mike MacFarland of Energy Docs in Redding, California. Mike reworked the numbers to accommodate the dry California climate. I decided to install a 1½ ton air conditioner (that’s 1 ton for every 1,255 square feet of floor area). I wasn’t certain about the furnace, though. My thoughts were to install a 45,000 Btu input two-stage 95% condensing furnace with an electronically commutated motor (ECM) blower motor, and to operate it on first stage only. I talked with Rick Chitwood of Chitwood Energy Management, Incorporated, Mount Shasta, California. Rick suggested a heat pump. I also talked with Andy Wahl of AC Home Performance, Incorporated, in Bay Point, California, who said the same. I was listening, but not convinced. Then Gavin Healy of Balance Point Home Performance in Grass Valley, California, asked me how I planned to get proper air mixing in each room with the low-velocity air delivery of the 45,000 Btu furnace running on first stage. After coming up with several creative ideas, I decided that it was impossible. The heat pump won.
A 2-ton, 16-SEER, R-410A, two-stage heat pump with no backup heat (heat that comes on during the defrost cycle) was installed, matched with a 3-ton air handler with an ECM motor. The second stage is locked out by setting the dead band in the thermostat to 10°F, so the unit is operating at 1.4 tons, or roughly 17.000 Btu. That’s 1 ton for every 1,345 square feet of floor area, which destroys the 1 ton for every 500–600 square feet rule of thumb.
Next I called my friend Tom Danielsen of Danielsen Construction & Energy Management in Angels Camp, California. Here’s where the real journey begins. Tom put me in contact with Bill Soest, a HERS II Rater with Evergreen Technologies in Angels Camp, to do the Energy Pro rating in order to have this job qualify for Energy Upgrade California. The furnace and evaporator coil were removed from the attic. We discovered that the flex duct was a combination of R-6 and R-4.2. The flex duct was removed and replaced with R-8. We looked at the number of supply registers in the house and at their location. We decided to remove three supplies and relocate four of the remaining seven. This reduced the exposed duct length by over 100 feet in the attic. The original supply registers were replaced with curved-blade Shoemaker grilles, which throw the air 75% of the distance from the register to the far wall for good air mixture and to keep the airflow off of the occupants—namely my bride, Luci, and me.
The next step was to install baffles to prevent blown-in insulation from covering the soffit vents. The perimeter top plates were air sealed with a Froth-Pak of expanding foam. The crew then wandered all over the attic, sealing every penetration they could find. Three significant air leaks were found—one over a bookcase in the hall, one by the fireplace insert, and one by the range hood vent to outside.
Bath fans were replaced with Panasonic Whisper Green fans and were routed through the HRV. The bath fans are pulling 83 CFM measured and set to a 20-minute off delay.
The original furnace location was not ideal for optimum air delivery, so the new air handler was relocated to provide shorter duct runs. This also allowed for insulating beneath the air handler platform, which the original location did not.
The original equipment manufacturer’s Thermostatic Expansion Valve (TXV) in the air handler was removed, and an adjustable TXV was installed outside the cabinet for ease of adjustment. The heat pump was installed, leak checked, and double-evacuated, and the tuning began. The liquid line in the attic was insulated. The system turned out to deliver 740 CFM on first stage with an external static pressure of 0.23 IWC. This is 528 CFM/ton. Superheat running on second stage at the air handler was 3.5°F, superheat at the heat pump was 7–9°F, and the subcooling was 5–7°F. These numbers at the heat pump are at manufacturer’s specifications.
It was now time for a blower door and duct test. The blower door came in at 1,032 CFM50, a 45% reduction in infiltration. We decided to stop there, because there is an open-combustion natural-draft water heater in the attached garage. We performed a maximum house depressurization test, which measured 4.8 Pa negative in reference to outside at the water heater. This confirmed that shell sealing is complete. A multiday CO2 test showed 794 ppm with the HRV off and 470 ppm with the HRV on low speed delivering 60 CFM. Duct testing came in at 20 CFM25 to the outside, a little less than 2% duct leakage. Not bad.
After final commissioning of the HVAC system, which includes adjusting delivered airflow for each room, the insulation in the attic was built up to R-60. All R-8 ducts rest on the floor of the attic and are covered with 18 inches of cellulose.
We changed most lighting to LEDs, CFLs, and T-5 or T-8 fluorescents. The outside landscape LED lights are controlled by a photoelectric cell switch. The laundry room T-8 light is controlled by an occupancy sensor light switch. We added 1.28 gpf toilets, 1 gpm faucet aerators, and a Metlund on-demand recirculating pump to bring hot water to the kitchen faucet. The externally insulated water heater temp is set to 120°F. We also added 90% shade screens to the west-facing windows.
The thermostat is set at 70°F in the heating season and 75°F in the cooling season. We do not use a setback setting.
So what did we get from this project? Even temperatures in each room, no air blowing on us, dusting furniture every four months instead of every month, and a total annual energy reduction of 46%.
What Did I Learn?
This was not rocket science. This was proper testing and designing, along with meticulous installation practices. It is imperative to learn what the building is doing before you decide which HVAC equipment to install. Once you have learned the house, correct the faults that you discover through testing—namely, air leaks and insulation insufficiencies. Learn how much heat leaves each room on the coldest winter days and how much heat enters each room on the warmest summer days. Learn how much internal heat is produced in the house with appliances and lighting. By determining the room-by-room heat loss and heat gain and internal loads you can design the distribution system, which consists of the ducts, supply register locations, and register design and performance. By adding up the heat gain and heat loss for each room, you know the size of the system required to meet the needs of the building. Be conservative. Round down on size, not up.
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Once the equipment has been installed, testing and commissioning comes next. CFM delivery to each room must be measured and adjusted to meet design specifications. Total airflow must be measured to confirm that the external static pressure is within the manufacturer’s recommended range. Refrigerant system measurements must be performed to confirm that the superheat and subcooling numbers meet the manufacturer’s specifications. Temperature splits and BTU delivery must be measured.
What you will get is a system that delivers comfort throughout the entire house at minimal cost, and an operation that you can’t hear when it’s running. We are enjoying the results.
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