Patent Application
20240133565
The present invention relates generally to the field of forced air HVAC systems, and improving the installed capacity and operational efficiency of said heating, ventilating, air-conditioning and ductwork systems, for residential and light commercial environmental comfort systems. A residential or light commercial HVAC (heating, ventilation, and/or air-conditioning) system controls environmental parameters, such as temperature, humidity and indoor air-quality of a building.
Nationwide research studies spanning 25-years have confirmed that over 50% of HVAC systems in operation today are not properly installed or maintained according to HVAC equipment manufacturer's specifications, and fail to achieve rated capacity and potential efficiency. Numerous government and utility funded field-studies further estimate that upwards of 100-million HVAC systems in operation today have numerous technical system faults that reduce overall performance.
A major driver of interest in home energy audits and energy efficiency retrofits for single family homes, are a result of discomfort related to overheated upper floors in the summertime, and cold rooms in the winter. The vast majority of these uncomfortable homes are 3-story, and built from the 1980's-2010's.
The most common fault affecting air-conditioning performance is inadequate airflow over the indoor evaporator coil, due to overly restrictive ducts and filters on the return-air side of the air-handler's ducts. Our extensive work in the field of energy audits and retrofits has determined that one primary reason for building temperature stratification in summer (65° basement, 75° main floor, 80°+upstairs), is inadequate air-flow through the ductwork, resulting in less cooling delivered to the upstairs, and lower overall AC-system cooling capacity and efficiency. Additionally, in winter, less heating is being delivered via ductwork to rooms the greatest distance from the furnace, such as rooms over garages in 3-story homes.
The buildings share a common design flaw in the HVAC system: inadequate return-airflow due to elevated negative static-pressure caused by overly restrictive 1″ wide filters, installed when the home was originally built, or not corrected during subsequent HVAC equipment installations. Shelf-space for furnace-filters at big box retail hardware stores appear to indicate that 1″ wide filters, versus the much less restrictive larger & wider filters, are still in use in 90% (or more) of homes.
Homeowners and renters attempt to mitigate overheating upper floors by using the air-conditioning excessively, and/or running the air-handler (furnace fan) continuously. Both practices fail to solve the problem, cause unnecessarily stress on HVAC systems, and increase energy consumption, often during peak electricity demand hours. Service calls for repairs also increase, and equipment lifespan is shortened.
Building owners and contractors will often misdiagnose the root cause of climate-control problems, and higher utility bills, by attempting to resolve these issues with more expensive energy-retrofits, including: redundant insulation levels, replacement windows, and premature retirement of existing HVAC systems.
When residential building codes for new-construction require HVAC systems to be designed using computer-aided duct design software, the use of 1″ wide filters in new construction have virtually been eliminated. Likewise, high-efficiency HVAC systems installed through utility sponsored rebate programs also require better air-flow to achieve optimized heating & cooling capacity and efficiency. In both cases, large 4″×20″×25″ filters are used to reduce air-flow resistance by increasing the surface area of the filter.
Forced-air heating and cooling systems utilize airflow over heat exchangers and evaporative cooling coils to add or remove heat from buildings. Both processes depend on adequate volume of airflow to meet manufacturer's design specifications, and rated output, usually measured in British thermal units (BTUs).
Heating=Cubic feet of airflow(CFMs)×Air Temperature Change(delta-T)×1.09=BTUs output
Cooling=Cubic feet of airflow(CFMs)×(Enthalpy of leaving air−Enthalpy of entering air)×4.5
Resistance to airflow through ductwork is measured by static-pressure with a manometer, and usually in inches of water column (i.w.c.) or in pascals. The higher the static-pressure, the more work (energy) is required to force air through the ducts, and the longer effective-length of the ducts, the more resistance.
Efficient duct design reduces static-pressure and effective length by using ducting that has less resistance. Rounder and larger in dimension, shorter in length, smoother in bends and straighter in course, create less resistance. More rectangle and smaller in dimension, longer in length, sharper in bends, and crooked in course create more resistance. For example, smooth curves create less resistance than square 900 bends.
Efficient duct design also utilizes filtration systems that create less resistance and lower static-pressure. The more surface area of a given filter in said ductwork system, the less resistance to airflow.
Refrigerant-based, split central air-conditioning systems require 350 cubic feet per minute of airflow, per ton of cooling capacity in hot humid climates, and 450 CFMs per ton of cooling capacity in hot dry climates, in order to operate at full rated cooling capacity and efficiency. The majority of air-conditioning systems in use do not meet those targets, and performance declines as airflow declines. Furthermore, refrigerant charge can not be accurately adjusted if proper airflow levels are not achieved beforehand.
Blower motor and fan efficiency are measured in cubic feet per minute (CFM) of airflow per watt of energy consumption. Less restrictive duct and filter systems improve fan performance for this metric.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
This invention provides consumers and contractors with a simple, scalable, and inexpensive filtration solution to improve airflow in millions of existing residential and light commercial HVAC systems. The filter modification invention takes about 1-hour to install, and cost approximately $100 in materials.
Our initial data set of before-and-after measurements, utilizing precise AC-system commissioning tools, demonstrated an increase of 8%-40% in cooling capacity and efficiency for homes with this low-cost filtration modification. A reduction of 50% in return-air static pressure, and an increase of 200-400 CFMs over the indoor coil is typically achieved. Most importantly for customers, reductions in upper floor temperatures of 3-7° is reported with no other system changes.
Estimated breakeven payback for these filter modifications is 24 months or less. Return on investment for the filter modifications could be as high as 900% or more, based on multiyear energy savings, increased equipment life and fewer annual filter changes. Even assuming very conservative improvements in HVAC efficiency, most homeowners can expect straight line payback of their investment 2× as fast as an incandescent to LED lightbulb conversion, heretofore the “gold standard” of financial payback for energy efficiency upgrades.
We have also found that the larger filters are less likely to be dirty or totally clogged, and restricting airflow, because they need less frequent changing; every 6-12 months vs 1-2 months for narrow filters.
The embodiments relate to the field of installing and maintaining building heating, cooling, and ventilation systems, and optimization of those HVAC systems.
Certain embodiments include, but are not limited to a method of replacing narrow and smaller dimension air-filters, which have higher resistance to airflow and cause reduced heating and cooling capacity and efficiency, with wider and larger dimension air-filters that are less restrictive to airflow, and increase heating and cooling capacity and efficiency, in forced-air heating and cooling systems in buildings.
A filter access-panel door constructed in accordance with one embodiment. The access-panel door is installed so that said access-panel can be used to close the filter access opening in the return-air ductwork, and removed when inspecting or replacing the HVAC system air filter. Said access-hatch will be installed in existing return-air plenum ductwork, covering a vertical, horizontal, and diagonal opening in said ductwork. Other embodiments include a technique, and the use of durable materials, for installing a filter installation and replacement access-hatch panel door to facilitate the use of less restrictive air-filters in forced-air HVAC systems.
An access-hatch door constructed in accordance with one embodiment, utilizes a handle used to grasp the filter access hatch for removal or reinstallation of access door.
A filter access hatch door retention device is used to secure access door to the return-air plenum ductwork, and allow for repeated installation and removal of said door, while minimizing airflow through said access-hatch. An outer-facing slot attaches to said existing return-air ductwork, and an inner-facing slot retains the access door, allowing for convenient installation and removal when needed to inspect or replace said filters.
A filter retention tray is constructed in accordance with one embodiment. Further embodiments include a technique, and the materials for installing a filter-retention device, mechanically fastened into said forced-air heating and cooling system return-air ductwork, to properly fasten larger filter into proper position, in order to achieve continuous, and dependable filtration of air-born particles with less resistance to airflow. Said filter retention tray is attached in the lower (bottom) outside corner of the return-air plenum ductwork in order to establish and maintain filtration of HVAC system airflow.
Operation and Procedures:
Building owners, occupants or HVAC technicians cut a vertical or horizontal slot in the face or surface of said return-air plenum ductwork, large enough to allow for the installation of larger, less-restrictive filters, and subsequent replacement of said filters when dirty or clogged with particles.
Building owners, occupants or technicians install filter access-panel retention devices on either side, and bottom of the new slot, such as S-lock or Z-lock, and other ductwork attachment devices, to allow for the convenient removal and replacement of said filter access-panel by homeowners or HVAC technicians.
Building owners, occupants or HVAC technicians mechanically fasten said filter-retention device, such as a sheet-metal tray or C-channel to existing return-air plenum ductwork, in order to maintain air-filter position and during blower fan operation in forced-air heating and cooling systems.
