Deciding to renovate and upgrade your HVAC system simultaneously is a major undertaking in itself. A well done job will provide comfort for another two decades, while a poor job will leave you patching up the same issues for 20 years to come.
Residential HVAC retrofits are rife with poor decisions at every stage – and the root cause of these problems usually stems from a single issue – treating the selection and specification of air conditioners and gas heating systems as a late-order decision and not an early design priority
These seven steps will help you avoid the most egregious HVAC retrofit mistakes.
One of the most common mistakes that a lot of homeowners and even HVAC contractors make is to base the selection of the new system on the size of the old one. A system that was oversized to compensate for a lack of insulation, windows, or poor architectural design will fail you miserably if its replacement is oversized as well.
Make sure you have a Manual J calculation (the industry standard) for your new system
This calculation takes into account all possible heat loss and gain for your home and is used to select the system that will allow you to maintain a comfortable temperature inside irrespective of the weather outside.
The oversized system will be short cycling and cause uncomfortable temperature variations, while an undersized system will be overworked and unable to reach your desired temperature in cold weather or cool your home adequately in the summer. Either mistake is prohibitively expensive at the time of retrofitting.
If your contractor wants to do a “guestimate” instead of a proper calculation, it should make you suspicious, so refuse to allow them.
It is impossible to retrofit properly without a proper duct assessment. Installing a high-efficiency furnace or HVAC system in a home with improperly sized and damaged ductwork is a mistake that will waste your time and money. A system that is oversized or improperly installed will produce uncomfortable temperatures and enormous utility bills. If the ductwork is undersized, the fan will not be able to deliver the required amount of conditioned air to the interior of the home.
A properly designed, well-sized ductwork should help the system to deliver a minimum of 90% of the heated and cooled air to the parts of the home that need it (DOE).
This issue is exacerbated when a homeowner replaces their old system with a new high-efficiency model without updating the ductwork. The improvement in performance and the ability to push more air through the ducts will cause the system to work overtime to compensate for the inadequacy of the ductwork, which will add thousands of dollars to the retrofit bill.
The test that is needed to assess the performance of the ductwork is called a static pressure test.
A qualified and professional HVAC technician will be able to test it for you at several pressure points, and a discussion of the results will be able to identify the cause of any imbalances. The causes should be fairly obvious – a reduction in the cross-section of the trunk duct, kinks in the flexible ducts, or the lack of proper mechanical seals at the duct joints.
Whatever the reason, your technician should be able to advise you on the best way to resolve the issue.
It is essential to have the duct test done before making a decision to replace your system, because the results directly impact the choice of the system, equipment size, and other factors that will greatly influence the cost of the retrofit.
The most common mistake that homeowners make during retrofitting is to forget that an air conditioning and heating system can only maintain one temperature in a house. An extreme example of such a retrofit mistake might include having a west-facing room and an east-facing room in your home. The west-facing room will get significantly hotter during the day because it will be exposed to direct sunlight, and the east-facing room will be warmer in the morning when the sun rises over the horizon and cooler later in the day. To retrofit such a home without designing a zoned temperature control system would be a mistake, as would be retrofitting a home with a basement, above-ground rooms, and ground-level rooms with a single temperature control system.
Zoned temperature control allows for different temperatures in different parts of the house. The most common example of such a system is a ducted HVAC system with zone dampers and thermostats. Another example is a ductless split system with multiple heads that can be placed strategically in the part of the house that need extra heating or cooling.
It is essential to emphasize that it is impossible to retrofit a zoned temperature control system to a home with existing ductwork. The system should be designed by an experienced professional from the ground up.
The primary purpose of the thermal envelope of a home is to protect the conditioned air inside the house from outside air temperatures and humidity. A thermal envelope consists of the building’s walls, roof, windows, and any other physical elements that are exposed to the outdoors (doors, etc.)
If the thermal envelope of a home allows warm air inside during winter and lets it all out during summer, the system installed in such a home will have to run constantly to compensate for the loss of heat during the winter and remove the excess during the summer. Retrofitting is an excellent opportunity to improve your home’s thermal envelope dramatically.
If the thermal envelope is optimized, it will reduce the size of the system that you need proportionally to the insulation performance of the materials used (R-value). It will also reduce your utility bills considerably because an optimized thermal envelope reduces the running costs of a heating and air conditioning system by as much as 30%.
There are two things that should be done to optimize the thermal envelope of a home.
First is to bring the R-value of walls and roofs to the standard level. That should be done while the walls are still accessible (during a renovation). Second, it is necessary to minimize the infiltration of outside air that comes through penetrations in the walls (doors, windows) as well as through ceiling fixtures and other weak spots. Thermal envelope optimization should be completed well before selecting the system that will be retrofitted.
The principles of passive solar design should also be used when renovating. They will help reduce the amount of energy required to heat the house in winter and cool it in summer by maximizing the amount of solar gain that can be redirected into the home.
The performance characteristics of the heating and air conditioning systems are determined by the climate they are used in. In other words, the systems that use gas, have no ductwork, utilize hydronic heating, or are reverse-cycle ready are ideal in some climates and utterly unsuitable in others. What works in New Zealand and Australia will not work in Canada and the United States.
The shift to all-electric, highly efficient heat pump systems is being driven by decarbonization and electrification goals that have been endorsed by policymakers worldwide. The latest generation of variable-speed compressors makes it possible for air-source heat pump systems to operate efficiently in a wide temperature range (including below freezing). The US Department of Energy estimates that modern ductless heat pump systems that utilize hyper-heat technology can operate efficiently down to -13 degrees Fahrenheit with a Coefficient of Performance (COP) ranging from 3 to 5.
This is a fancy way of saying that for every unit of electricity, the heat pump can generate 3 to 5 units of heating and cooling power. In simple terms, you can save a significant amount of money on heating and cooling by retrofitting to a modern reverse cycle ready HVAC system.
In places with extreme temperatures, such as Canberra, home improvements and renovations may require a reliable and efficient reverse-cycle heating system, and homeowners can explore Reverse Cycle Heating Services Canberra when planning the upgrade. Residents of places like Canberra have harsher winters and hotter summers than residents of, say, Adelaide. Therefore, it is essential to choose a system that will be able to maintain the temperature inside the house in both seasons.
Hydronic systems offer incredible value because of the ability to provide a stable source of radiant heat with virtually no air movement involved.
They help eliminate allergens and dust while providing even temperatures throughout the house, and they do not suffer from any of the drawbacks inherent to traditional ductwork. Hybrid systems that utilize heat pumps boast most of the advantages of traditional forced-air systems without all the drawbacks.
Modern HVAC systems including heat pumps have extremely high amperage draws. Upgrading to a new system usually means that you will have to upgrade your electrical panel in order to meet the demands of the new equipment. The standard electrical recommendation for all-electric homes in Australia is 200 amps. If you have plans to charge an electric vehicle in the future, you should take that into consideration when upgrading your electrical panel. Electrical services are much easier to upgrade during a retrofit when the walls are opened up and the general contractor is on site.
Variable refrigerant flow systems that utilize multi-split configurations have specific amperage requirements that should be calculated by both your HVAC contractor and your electrician. Failing to do so can lead to dangerous situations where electricity surges cause breakers to trip (and systems to be shut down) frequently. In addition to being a nuisance, frequent breaker trips can damage the equipment and void the warranty.
Sealing the air leaks in your home and insulating it with spray foam, vapour barriers, and energy-efficient windows will make it much more comfortable to live in. However, in doing so, you will deprive your home of the natural ventilation it previously had. The indoor air that you breathe and the water vapour from your showers have nowhere to go, and the stale, humid air that is generated inside has nowhere to escape.
Once the natural infiltration rate falls below the healthy level, the ventilation becomes a design and maintenance concern. Ventilation can be achieved by installing an exhaust fan that will remove the stale air from the interior of the house. However, if the air coming into the house is not tempered, it will ruin the comfort that you tried to achieve with all that insulation. The best way to ensure good indoor air quality and maintain the indoor temperature is to install an Energy Recovery Ventilator (ERV).
ERV or HRV (Heat Recovery Ventilator) will allow you to exchange the indoor air with the outside air while recovering the heat from the exhausted air. In effect, you will be able to reclaim the heat from the heated indoor air in the winter and cool the indoor air in the summer. Since ERVs also recover moisture from the exhausted air, they can be used to regulate the humidity in the house as well, which makes them ideal for installations in both temperate and tropical regions.
It should be evident from the list above that time is the most valuable resource for a homeowner during retrofitting. Every decision made before the renovation begins is a decision that saves money. The earlier the decisions are made, the more money you stand to save. It is critically important to involve your HVAC contractor in the early stages of the design process so that the finished product is something that everyone can be pleased with.
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