Majority of homes have systems in place to provide both heat and a cooling effect. Heating and cooling make up the largest portion of your energy bill. Temperature is not the only way that human comfort is determined. Humidity level and air movement also play a role. Therefore, simply adjusting the thermostat to the desired setting may not be the answer to your energy-saving goals.
Fans use less energy than air conditioners. In the summer, people like the feeling of moving air over their skin because the term “summer breeze” in of itself brings along a cooling effect. It is not the air temperature that you should be concerned with but the temperature of your skin. Therefore, fans can cool you down which they do through convection. Fans help improve ventilation but don’t cool the air; they provide a cooling effect.
Lower the Humidity
Humidity causes people to feel warmer on days that exhibit normal temperature levels because a higher wetness content in the air doesn’t carry heat away from the skin as effectively as dry air does. Therefore, a dehumidifier is a great option in the summertime and especially as an alternative to air conditioning. They use less money and are significantly cheaper regarding upfront investment.
If you don’t use a washer dryer machine to dry your clothes and use a clothesline instead, you should keep it in the garage because placing it inside the home will increase the humidity of the air and make you rely more heavily on on-air conditioning or dehumidification. However, you can adjust in the winter and bring the clothesline back into the house because it will help keep the warm air in and reduce heating costs.
You should have exhaust fans installed in every bathroom and kitchen in your home. This is because it will reduce the humidity levels. Humidity can also lead to yellow staining on your doors (given their painted white). You can install a humidistat to automatically turn on the exhaust vents once a certain humidity level is reached.
Heat Recovery Ventilators
Through the exhaust airflows, a portion of the heat is lost by every house that uses fuel for heat.
A heat recovery ventilator uses a heat exchanger to heat or cool incoming fresh air, which reduces the energy consumption of a ventilating system by more than 50 percent. There are heat recovery ventilators that have an added feature that exhaust moisture between indoor and outdoor air which is called energy recovery ventilation (ERV). The ERV takes incoming humid air and mixes it with exhaust air to lower the humidity level indoors. ERV is recommended for those living in high heat and high humidity environment and wants to reduce their dependency on large energy consuming systems such as air conditioners. So again, HRV is to improve heating whereas ERV enhances cooling.
HRVs and ERVs both use fans to circulate air indoors. They both also take fresh air and replace it with stale air so that the heating ventilation and air conditioning (HVAC) system is always in motion of displacement. Look for an HRV with two fans if you want a balanced between the exhaust (outgoing air) and intake (incoming air)
HRV is a heat exchanger at its core. The core is made up of plastic and aluminum plates. An ERV relies on several desiccants or permeable plates to transfer moisture-laden air. This core heat exchanger conducts electricity quickly and efficiently through its two ducts that are for exhaust and intake airflow. The two ducts remain separate in function meaning they don’t mix the air streams. Instead, heat from the exhaust air stream is used to increase or decrease the temperature level of the intake.
Heat Recovering Ventilation Sytem: Pros and Cons
There are several reasons to use an HRV or ERV depending on the primary climate type in the area within which you live. They are:
- The constant flow of fresh air creates a more comfortable and healthier environment.
- Newly built houses are designed to be airtight, but they need active moisture control to prevent the buildup of mold and mildew. An HRV helps in controlling that moisture.
- An HRV helps mitigate the effects of moisture in homes that are built with spray-foam insulation and structural insulated panels.
- Opening the windows or running an exhaust fan will help in the short term but rarely do they have an impact over the long term over air quality
- Adding an HRV to a new forced air system will cost about $2500, but the benefits over the long-term are worth the investment.
- Cost can be in the thousands of dollars
- Will require a HVAC professional to install.
Types of HRVs
There are five types of HRVs or mechanical heat recovery ventilators. They are a rotary thermal wheel, fixed plate heat exchanger, heat pipe, run-around, and phase change materials.
To start, a rotary thermal wheel is a mechanical way of recovering heat. It works by rotating a permeable metallic wheel that moves heat from one air stream to another air stream. It also stores a large amount of thermal energy mass within the wheel until it is transferred to a more cooling airflow channel. There are a heat wheel and a desiccant wheel which are the sub-types of the rotary thermal wheel.
A fixed plate heat exchanger is the most common type of HRV and works through a series of thin metal plates. Two separate air streams pass through the space between these plates, and the transfer of thermal energy occurs from the temperature of one plate to the other. It is the most recommended option because these devices have shown to be useful for 90% of the time at increasing heat utilization.
Heat pipes are a more traditional method of heat recovery because they use an evaporator and condenser with a sealed pipe that contains airflow that constantly changes phases to exchange heat temperatures — the fluid from the humidity changes to gas in the evaporator and reverts to fluid in the condenser.
Plain gravity, pressure, or wick forces are used to move the fluid and gas from one side to the other within the pipe.
A run-around system is a hybrid system that uses portions of the other types of heat recovery technologies to transfer thermal energy. It works through two different heat exchangers with two fixed plates made from metal. A pump works to keep the fluids moving in the right directions and while this is energy intensive its been proven to work better than air circulating fans.
Finally, we have the phase change materials. These are commonly referred to as PCM. PCMs are generally built into the structure of the house and are classified as latent heat storage units. Often it is found in the drywall, and there are thermal beads that melt and return to solid state depending on the temperature. Therefore, when it’s warm, you’ll experience a cooling effect and vice versa when the temperature drops.
Choosing the Best HRV
The type of HRVs you will find available in your area will depend on the local distributors and the climate in which you are based. Of course, you can order online, and have it shipped to you. There are different types of features you should look for and research further such as air quality sensors, air filters, and speed controls. You can also find independent test results conducted by the Home Ventilation Institute which provides performance ratings on HRV and ERV systems. You should always consult with a professional HVAC specialist that will inspect your home and recommend a system specific to your building’s design.
Regarding installation, there are also a wide variety of options to choose from. Hydronic and radiant systems may not be compatible as HRVs and ERVs are most commonly used with forced air systems. HRVs are installed as whole-house units, but some options restrict use to a single room or so. This window-based HRV is more cost friendly and portable to use.
Here are some tips when working with an HVAC installer and new HRV system:
- Place each return outlet near the ceiling and away from a range or stove.
- The shortest route should be used, and ducting should be smooth and round.
- Fresh air intake should be away from chimneys and exhaust air valves
- Fan component should be installed in a convenient place where it is easy to clean, maintain, and repair.
- If condensation is likely to accumulate, a drain should be installed to keep moisture away from the heat exchanger.
- Seal joints that connect ducts to plenums, tees, wyes, registers, etc.
- Ducts that pass through uninsulated areas should be insulated in of themselves.
- A separate supply inlet should be used for each bedroom and each shared space such as a living room
- A separate return outlet in rooms with high humidity such as bathrooms should be installed.
Some notable brands that manufacture and install HRV systems include Zehnder, vanEE, Life Breath, and Renew Aire.
What about Portable Heaters and Humidifiers?
Portable heaters can be moved around to any position. However, they have fans that move air over a resistance coil, so they provide a counterintuitive effect that both warms and cools a room. The best choice is to use a radiative type of heater, one with parabolic reflectors with the heating core at the focal point.
These types of heaters spread heat by radiating instead of convection. It does, however, have more safety risks, especially around children so be sure to read the warning label.
Additional HVAC Tips to Consider with using an HRV
- If you have a combustion HVAC system, you should get it inspected by a professional HVAC installer every few years because carbon and soot can buildup in the chambers. Other types of systems such as solar/space heaters and heat pumps are good for at least ten years or so before they need servicing.
- Make sure your air filters are clean because HVAC systems need adequate airflow to work efficiently. Clogged filters will perform worse and use more energy to work.
- Avoid maze-like ductwork. Ductwork that has too many bends and turns will use more energy because the pumps or fans will need to work harder to push the air through the turns versus a straight pipe that tends to be more efficient.
- Consider louvers for rooms that are closed-off. This will ensure there is enough air flow for a forced-air system to work.
- Filters, fins, and coils can be susceptible to debris buildup. As a result, you can take off the lid on your condenser and pressure wash it to remove the excess dirt.
- When fixing joints, use aluminum tape instead of duct tape and always wear a face mask to avoid dust from entering your respiratory system
In conclusion, an HRV system is an effective way to reduce your energy bill and improve air circulation in your home. It may cost a bit up front, but the payoff is significant regarding the air quality freshness and the amount you’ll save on your energy bills over the years. It’s also important to consider a heat recovery ventilator system if you are building your home from the ground-up. If you intend on replacing the entire HVAC system in your house, the best bet is to contact an HVAC service company for a full inspection and quote. You should, however, use the information you learned here to help you in making your decision. Also, remember that replacing an HVAC system is a long-term investment and you should try the simpler DIY adjustments before making big changes.