Modern Mechanicals—

HVAC System Choices Are Only Part of the Energy Use Equation

Home heating and cooling systems consume more energy than any other home system, accounting for nearly one-third of a home’s utility bill. While equipment choices do play a role in reducing energy consumption, your HVAC system choice is only one part of the equation.

Building material selections and best practices that provide a more constant building temperature to reduce the need for high-powered heating and cooling systems are the first step. Proper load calculations are a critical next step. When it gets down to the point of comparing HVAC equipment, the most hotly contested discussion would be based on the type of fuel used to power your equipment. (That is, where there is still a choice to make).

As an increasing number of local municipalities are considering bans on residential gas hookups, many states have passed or introduced measures that would prevent local measures from blocking access to utility service based on fuel type. Proponents of the gas ban would argue that, just like in the automotive world, the “clean energy” concept means the move to all-electric is imminent, whether we’re talking about vehicles or homes. Adding even more burden to our already taxed and high pollution-generating power plants by banning the use of natural gas is not the answer to reducing greenhouse emissions, say opponents to natural gas banning.


You must consider that when a furnace burns gas, it’s using a primary energy source. Heat is produced by the combustion from burning a fuel. When electricity is used for heating or cooling, the electricity is just a carrier. The primary energy in that electricity comes from a secondary energy source. The secondary energy source most often comes from burning gas or coal or harvesting it from a controlled nuclear reaction (via a nuclear power plant).

The rising costs of electricity and the failures of electric grids are other big picture considerations.  These are the very reasons why some engineering teams are introducing alternatives to electrically driven A/C units.   Thermally driven chillers such as used on A/C units by Chromasun, an Australian company, operate on solar thermal energy to drive them while supplementing with natural gas energy when needed.   An ice-powered A/C system called the Ice Bear is proving its merit, essentially by freezing water in a tank overnight during an “ice charging” mode.  In “ice cooling” mode, the ice provides cooling for up to six hours, after which, a conventional commercial air conditioner takes over.  Whether you’re using solar or ice, or taming the kinetic energy of wind or water, these technologies are still going to need a gas or electric back-up, so here we go again with the arguments, which are often politically motivated.


Electric heating and cooling has become more efficient and more viable for use across even the most challenging climates, thanks to heat pump technology. Heat pumps use electricity to run mechanical equipment that moves heat from one place to another. When connected to multiple indoor units, the heat pump system would be called a multi-split. However, an outdoor unit connected to a single indoor unit (one-to-one) provides the best efficiency.

One-to-one “mini-split” systems were originally introduced as lower capacity split system heat pumps used for heating or cooling, or both. Just like “compact” trucks, “mini-splits” seem to keep getting bigger; you can get mini-splits with capacity up to 4 tons.

Indoor units come in wall-mount, ceiling cassettes and floor-mounted models and may be ducted or ductless. Most mini-splits have inverter-driven compressors with variable capacity and show much promise in the future of high-performance homes due to their high efficiency and ability to ramp down to very low-capacity values. Lower capacity allows heating and cooling to be zoned using separate pieces of equipment.

Geothermal is another fossil-free option making use of the natural stability of below-ground temperatures to provide a baseline for the home’s indoor temperatures. Combine the geothermal system with renewable energy to power the pumps and electrical equipment, and the system easily becomes net zero. While Geothermal HVAC has long been considered a highly efficient alternative, high up-front installation costs and space limitations have been obstacles. A large open lot where conventional drilling equipment could access and maneuver freely generally limited ground-based geothermal to rural areas. New compact and agile sonic drilling rigs are changing this.

Like hybrid cars, maybe a dual-fuel heat pump is the perfect solution? At low temperatures, the pump draws on gas heat to maximize efficiency. When the temperature rises above 35 degrees, electricity takes over. Most of the time, when temperatures are above 35-degrees, the electric heat pump will warm and cool the home.


When you’re thinking about heating, it’s not just the air to think about, but also water heating, While newer, more energy efficient tank style water heaters convert a higher percentage of energy into heat and lose less heat through standby, the overall design of the traditional water heater still wastes energy by keeping the hot water ready for use at all times, and it loses heat travelling through the pipes to get to you.

Tankless or on demand water heaters have become a favorite alternative, but a true environmentalist will also weigh the fact that tankless heaters take significantly longer to deliver hot water than regular tanks. Other factors to consider are higher initial cost, flow rate capacities, maintenance, and warranty. Air supply ducts and specialized exhausts have a tendency to get blocked. Mineral build up, especially in hard water areas, has caused problems.

Even when using on-demand water heating, the EPA statistic says the average home wastes 12,000 gallons of water every year just waiting the two to four minutes average for that water to warm up. Products that address ways to avoid this shameful waste include point-of-use tankless water heaters, such as EcoSmart®, installed near a faucet or shower work to heat the cold-tepid water coming through the pipe run, immediately providing an immediate and endless flow of hot water. When the water finally does get heated, it is typically briefly used before flowing down the drain.


Drain water heat recovery systems, such as ecodrain® recirculate otherwise-wasted water back into the system. The process relies on a series of heat exchangers that strip the heat energy from the outgoing water and use it to heat more water in the future.

HotSpot® heat recovery units recover concentrated high temperature heat from your air conditioner’s condenser circuit, pumping the recovered heat directly into your hot water tank. Free hot water heating during the season that the air conditioning operates is a benefit. Heat pump users not only get free hot water during the cooling season but can also save up to 70 percent on water heating costs during the heating season. As a byproduct of removing the heat, HotSpot lowers the head pressure of the compressor creating an efficiency improvement of up to 18 percent.

GeoSolar Technologes (GST) is a Colorado-based climate-tech company that built the GEOS Neighborhood.  The community of new energy-efficient, all-electric homes have no gas bills, minimal electric bills, and enjoy the benefit of improved indoor air quality and low carbon emissions.  The community is also boasting of having no Covid-19 cases in the neighborhood throughout the pandemic due to the smart ventilation air purification systems in the homes that monitor CO2/oxygen ration and remove microbes and viruses. 


New HVAC technologies which use an Internet of Things (IoT) system are embedded with sensors, software, and connectivity to enable the HVAC system to exchange data with other connected devices pave the way for significant improvements that will not only save money on utility bills, but also reduce waste. Ecovent, for example, enables homeowners to digitally control the climate in every room of their home through an app. Smart sensors that gather and transmit climate data in every room, sending the data to the Ecovent Smart Hub which then coordinates with each vent, telling it to open or close, in order to direct airflow. This HVAC technology solves the dramatic temperature differences between rooms that results in inefficient heating and cooling, offering greater comfort with up to 30 percent savings on energy.

IoT systems also improve preventative maintenance by sensing data on air quality and equipment status. Even slight deviations from a manufacturer’s specification can lead to a large increase in energy consumption. The HVAC innovations with remote monitoring and diagnostics minimize power waste by ensuring units operate at their peak efficiency.

Gas burning in a modern water heater is an example of a primary energy source.  Heat is produced by the combustion from burning a fuel. 
But is reliance on more powerplants to produce energy for fueling electric power the best answer?
AiroDoctor® V10P-AC, an air purification kit for cassette AC units, makes it possible to easily upgrade air-conditioning systems with a powerful antibacterial and antiviral UV photocatalytic filter.


Careful management to avoid wasted heat is the name of the game in ventilation. While air-sealing and advanced technologies may lessen the AC tonnage needed and the BTUs required from the furnace, more proficiency in sealing gaps, cracks, and holes in the building envelope make proper ventilation essential.

Where there are separate fans to bring in fresh air and exhaust indoor air to the outside, the fans can be located together and alongside an air-to-air heat exchanger. These types of air-to-air heat exchangers are commonly referred to as heat-recovery ventilators (HRVs). An energy-recovery ventilator (ERV) works similarly to an HRV, recovering not only heat, but also humidity, generally making ERVs the better solution for hot and humid climates.

Getting a home with the latest in ventilation technology for better indoor air quality (IAQ) is a valid reason why some buyers will choose to buy a new home over an existing one. Awareness has been heightened for some time about the off-gassing of volatile organic compounds (VOCs), formaldehyde, flame retardants, and other chemicals prevalent in building materials, furnishings and cleaning substances.

The EPA also acknowledges that improved IAQ could help prevent the spread of COVID as well as other virus, allergies and even chronic diseases associated with poor IAQ. Mechanical ventilation, to bring in fresh air and get rid of stale air, is generally agreed upon as necessary equipment for a modern built home.

By operating an exhaust-only fan either continuously or intermittently to exhaust stale air and moisture, a modest negative pressure in the house is created, and fresh air is introduced either through cracks or through strategically placed make-up air inlets.

The negative pressure can, however, pull in other types of gases from the outside that we don’t want in houses. Supply-only ventilation uses a fan to bring in fresh air, anticipating that stale air will escape through cracks or designated air-leakage sites in the house. The incoming air supply if often supplied to the ducted distribution system of a forced-air heating system for dispersal.

A supply-only ventilation system pressurizes a house, which can be a good thing in keeping radon and other contaminants from entering the house, but poses the risk of trapping moisture-laden air in wall and ceiling cavities where condensation and moisture problems can occur.
The best solution is a balanced ventilation system using separate fans to drive both incoming and exhausting airflow allows control of where the fresh air comes from, where that fresh air is delivered, and from where exhaust air is drawn. Balanced ventilation systems can include an aforementioned air-to-air heat exchanger so that the outgoing house air will precondition the incoming outdoor air.

Take all measures to reduce your energy demand. Start with design and material selection and use best practices to build a tightly sealed home to cut back on the fuel or electricity needed to run the HVAC system you choose. Use the latest technologies to improve air quality while harvesting and reusing conditioned air and water. Add IoT systems to maximize control over your home systems. Take the time to educate your buyers about these decisions, illustrating your dedication to do more than just use it as a selling point. Instead, sell the long-term benefits, which include not only the buyer’s savings, comfort and health, but also those that responsibly benefit future generations.

Read / print this article as appeared in Building Savvy magazine

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