Category: Energy Efficient Design

What makes plumbing worthy of attention in an energy efficient house is the potential for water and energy savings. Heating water for domestic use accounts for a significant amount of energy use for most U.S. homes, about 17 percent of overall residential energy consumption according to the U.S. Department of Energy. It is estimated that the average U.S. household uses 350 gallons of water per day. Bathing, flushing, laundry, dishwashing, it all adds up, especially where older, inefficient fixtures are still in use. In some parts of the U.S. and the globe, the supply of drinkable water is already a problem. Increased population and changing climate is bound to put additional pressure on water resources, so it makes sense to implement water conservation measures now.

To keep hot and cold water use to a minimum, the following design guidelines can be effective: low flow shower heads and faucets, high efficiency and energy conserving washing machines, dishwashers and toilets, plumbing layouts that keep plumbing runs short, insulated hot water lines and on demand water circulation systems that eliminate the wait for hot water at the shower and sink. For the water piping material, cross linked polyethelene (PEX) can be a good green alternative to copper. It is less resource intensive than copper, easy to install, durable and can provide better water flow (no 90 degree pipe bends).

Regarding the domestic hot water heater, there are several options available: conventional electric or gas fired tank type, on demand tankless, indirect tank type heated by a boiler, or external solar collectors. Each has their own pros and cons. Conventional tank types have the lowest upfront cost, but they have standby energy losses as unused hot water cools in the tank. Tankless heaters nearly eliminate standby losses, but can be 3-4 times more expensive than a tank model. Indirect heaters heat water by using a radiant heating system”s boiler. They are durable and long lasting, but the boiler has to run during the summer. Solar collectors are a choice for those seeking to achieve net zero energy use. The energy is clean and renewable. However these systems are the most expensive and work best in warm, sunny climates. They also require back up systems in case the sunlight is inadequate to heat the water. So the choice of a hot water heater is often done in tandem with the type of heating, ventilating and air conditioning (HVAC) system the house is equipped with.

For our subject house, we are using a forced air HVAC system. A conventional gas fired water heater works well with this system. An extra insulated R-15 tank will reduce standby losses and the heater will be sized properly to avoid the storage of excess hot water. For a three bedroom 2.5 bath home the size is 40-50 gallons. It will be a high efficiency, direct vent through the wall, with a high energy factor rating of at least 0.60. We will use the water saving design techniques described previously to conserve water and energy.

An HVAC system works best when it is designed according to the local climate and the energy saving features of the home’s design. Features such as solar orientation, passive solar design, building envelope insulation, reduced air leakage, window and door design and placement should reduce cooling and heating loads. The result should be an HVAC system as small as possible. Systems that are sized too large use more energy than necessary and don’t function well because they tend to cycle on and off too quickly. The HVAC designer must perform heat loss calculation taking into consideration the energy saving features of the house to size a system that is just large enough.

There are several types of HVAC systems to choose from. To deliver heat, there are three basic systems: ducted forced air, radiant hot water radiators, baseboards or in floor tubing, and electric baseboards or panels. To produce the heat, once again there are many options, both in how the heating units work and what kind of fuel they use. Options include furnaces and boilers that burn fossil fuels such as natural gas, propane, or fuel oil, heaters that burn wood or pellet fuel, electrical heating elements, and air or ground source (geothermal) heat pumps,

An important aspect to consider is how effectively the device uses fuel. There are units that operate at efficiencies of 90 percent or more, meaning that only 10 percent or less of the heat potential in the fuel is wasted.

Air conditioning to cool the air is generally a must in climates with hot and humid conditions. As with heating, it is important to size the system correctly based on the actual cooling load for a highly insulated, air tight house. The system needs to avoid short on-off cycles so that air flows long enough to remove excess humidity.

The downside of air conditioning is its high electrical energy use, so the more efficient the system, the better. Efficiency is rated by a seasonal energy efficiency ratio (SEER) which is the cooling output in Btu divided by the power input in watt hours over the course of a normal cooling season. The higher the SEER, the more efficient the unit operates. Minimum SEER should be 13. Central air conditioning ideally requires ductwork to transport the air. Where ductwork does not exist, it’s possible to use a ductless mini split system with an outdoor compressor serving air handlers in several rooms.

Ventilation is a critical part of indoor air quality, especially in a tightly sealed building envelope. Stale air needs to be removed and fresh air brought in. Besides natural ventilation, there are three ways to provide mechanical ventilation. They are exhaust, supply and balanced systems.

Simple exhaust systems are what most homes have. Exhaust fans in the bathrooms and kitchen pull stale or polluted air out of the house. Make up air comes from air leaks in the envelope. In an airtight house this can be a problem due to the potential of back drafting flue gases from the heating system.

Supply systems, commonly found in forced air systems, include a fan that draws in outside air and circulates it via the air ducts. This pressurizes the home slightly

A balanced system creates neutral pressure by exhausting the same amount of air that it draws in. This is the ideal condition.

What about exhausting all that tempered air? Seems like a waste of energy. There is an energy price to pay for fresh air. A way to minimize energy losses is to use a heat recovery ventilator (HRV). In an HRV, incoming and outgoing air pass by each other through a heat exchanger without mingling. In winter, as much as 80 percent of the heat in outgoing air is transferred to the fresh cold air pulled into the house. The reverse occurs in the summer. HRV’s make sense for tight, super insulated homes that need a reliable source of fresh air.

Air filtration is also an issue. A wide range of filters exist, from simple fiberglass to HEPA. Filtration capacity is rated in MERV’s. The higher the number, the smaller the particles it removes. A range of 7 to 12 is appropriate for most houses, a higher range may be needed for persons with allergies.

For times when air is too dry, a central humidification system can be placed in a forced air system to keep relative humidity between 25 to 50 percent.

Regarding ductwork in forced air systems, ducts should be run in conditioned space. All joints need to be sealed with mastic to prevent air leakage.

Finally, the system should be controlled by a programmable thermostat or home automation system that can be set to automatically turn down the system when full capacity is not needed, such as when the home owner is away.

For this article I won’t describe geothermal heating and cooling since it has been decided not to use this type of system for the subject house. I am planning on covering the subject in a separate article.

So on to our subject house. For heating we are using a 95 percent high efficiency gas fired forced air furnace with direct through wall venting. Cooling will be an 16 SEER central air conditioning split system with outdoor compressor and condenser coil and evaporator inside. The system will have a 4 1/2 inch filter. There will be a central humidification system. The system will utilize a heat recovery ventilator tied into a whole house ventilation system. System control will be by a programmable thermostat.

One of the things we Americans take for granted is the ready availability of electricity. It’s estimated that one third of the world’s population still has no access to electricity. It takes a lot of work and energy to generate electricity. Power plants burning fossil fuels contribute heavily to the rise in greenhouse gases. Our appetite for ever increasing amounts of electrical power continues to rise. Today, lighting, cooling and heating consume 67 percent of all the electricity that’s generated. While power generation from solar and wind is increasing, the cost is still high compared to coal power, though costs are coming down as technology and infrastructure improves. For the present time, strategies for conserving electric use are an economical way to ensure there will be adequate supplies for the future without building a new coal fired or nuclear power plant in your backyard.

High efficiency lighting and appliances, along with house designs that increase the use of natural light can significantly cut residential electrical use. For lighting, the incandescent bulb has been the standard. It’s not very energy efficient and it produces a lot of heat. Alternatives such as compact fluorescent bulbs (CFL) use 75 percent less energy, last six times longer and generate less heat. Initially, the quality of light was poor with CFLs, but manufacturers have improved the light quality, referred to as color temperatures. Dimmable CFLs are also now available. Even more efficient than CFLs are light emitting diodes (LED). They use 90 percent less energy than equivalent incandescent bulbs and last about 100,000 hours before failing.

Good lighting design can go a long way to conserve electrical energy. Natural light should be the first choice for daytime use. Well placed windows can allow light into all rooms so ideally no lighting energy is needed until the sun goes down. At night, a mix of different light sources can be beneficial. Adjusting the level of light to match Certainly, it&#8217s something that should be taken into consideration, designed for the condition&#8217s equine racing industry, that has been on the steep path towards obscurity previously decades, getting lost the majority of its luster to save energy. For example, in a kitchen, bright undercabinet lights can help for food prep while recessed ceiling lights on dimmers provide general ambient lighting. The different sources can be turned on or off as needed. The use of lighting controls such as dimmers or occupancy sensors or timers to turn off lights can also cut energy use. For outdoor lighting, low voltage lighting systems and solar powered lighting can be good options.

What about solar and wind power generation? For wind power, you need enough steady wind to make the system feasible. The American Wind Energy Association says the economics of buying a wind generator begin to make sense when the average wind speed is 10 mph and utility power costs are at least 10 cents a kilowatt hour (kWH). Depending on the average wind speed, you need a turbine rated at between 5 – 15 kilowatts to make a significant contribution to the 9400 kWH of electricity the average American home uses. A 1 kilowatt generator can cost over $10,000, making wind an expensive option. Also, in many urban areas, wind turbines are restricted by the zoning ordinance.

Solar power can be generated by photovoltaic (PV) panels. When a photon of sunlight is absorbed by a PV cell, an electron is dislodged, creating an electric current. The cost of PV systems are still high. The cost is measured in “levelized” costs per kWH, which is the cost of the system over its lifetime divided by the total lifetime electrical output. According to the US Dept. of Energy, the levelized cost is now about 30 cents per kWH. Electrical cost in the Chicago area from the utility companies is running around 8 cents or less per kWH. PV is still expensive unless there are government subsidies to offset cost. A benefit to utility companies is that solar power works best during times of peak demand, that is, during the day. Reducing peak demand load to the utility can reduce the utilities’ need to provide additional power generation for peak demand periods, a benefit to the utility and the environment.

Appliances should be energy efficient, carrying the Energy Star label. A source of energy leakage are electronic devices such as security systems, cable boxes, televisions, computers, anything that operates in an instant on power mode. They draw phantom loads because they draw power even when they appear to be turned off. These devices ideally should be on power strips that can be completely turned off.

For our subject house, we will be using the electrical conservation strategies described above. This includes daylighting design, high efficiency light fixtures and appliances. Solar electrical power will not be pursued at the present, but a 1” electrical conduit will be roughed in from the roof to the electrical panel for future use when solar power becomes more cost effective.

One of the benefits of energy efficient design is an air tight, well insulated house that provides thermal comfort and lower energy bills. Choosing green interior finishes doesn’t necessarily offer the same type of economic payback. Decisions about these finishes are important however for their potential to provide a healthy interior that won’t cause illness or allergies and an opportunity to use materials with a low environmental impact. Here are some of the main considerations in choosing green finishes.

Toxicity: Some products emit unpleasant and sometimes dangerous fumes that can last long after occupants have moved in. They should be avoided.

Durability: Materials that hold up to hard wear reduce the frequency of repair or replacement and lessen waste.

Resource conservation: Reusing salvaged or recycled material means fewer resources have to be used to make new materials.

Sustainability: Building materials that come from easily renewable resources have less long term impact on the environment.

In choosing materials, one should consider the context in which they will be used. There are trade offs. For example, as a rule, less toxic alternatives should be used instead of more toxic. However, if a more toxic alternative provides a more durable finish, say oil based finish versus water based, and it can be applied in a way that won’t affect the occupants, it could prove to be the best choice because of its durability.

Other considerations include the following: Materials should be produced in the least disruptive manner possible. It’s best if they can be recycled at the end of their useful life. The application should be durable. The “embodied energy” which is the energy used to make a product, should be low. The product should not contain high amounts of volatile organic compounds (VOC), which are chemicals that easily convert to gas at room temperature. And wood products and adhesives should not contain urea formaldehyde.

The following are some of the green finishes available today and their pros and cons.

Paints and finishes made with low VOCs have reduced VOC off gassing. They generally cost more than standard products.

Natural clay plaster with integral color is an alternative to paint and does not contain VOCs. It costs more than paint.

Water based wood finishes have lower VOC content than solvent based finishes. Some people don’t like the appearance of the finish compared to solvent based finish.

Low VOC adhesives and caulks such as urethane based adhesives are less toxic than solvent based and have less VOCs.

Interior Cabinet construction uses particle board cores without formaldehyde based binders. Cabinet faces use wood certified as being harvested from a sustainable source. Use of wood veneer in lieu of solid wood conserves resources. Cost may be higher than standard materials.

Countertops made with plastic laminate, solid surfacing, stainless steel, tile, wood, natural stone and concrete are all options. Materials which are durable, don’t contain formaldehyde wood substrates and have low embodied energy are good green options.

Flooring such as finished concrete, linoleum, vinyl, bamboo, FSC certified wood flooring in solid wood and engineered prefinished varieties, cork, natural carpet, synthetic carpet, tile, rubber and reclaimed wood are all options. Considerations about flooring include durability, non toxicity, renewable sourcing and low embodied energy. Vinyl and synthetic carpet are manufactured from toxic materials and have high VOC off gassing. Many carpet companies are addressing the issue by creating products with green label certification with reduced VOC emissions.

The marketplace is creating a variety of products that are less toxic, more durable, conserve resources and are sourced from sustainable sources. By weighing the options you can choose finishes that are healthier, have a low environmental impact and are aesthetically pleasing.