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ARCH-TECH TIP EDITION 2 / SUMMER 2009

Horizon Archi-Tech Tips

Tip #3: Horizon's HVAC Design Criteria vs. Other Builders

The heating and cooling system must be designed carefully. It must be “right-sized”—not too big, not too small, just right (kind of like porridge). If it is too big, it will short cycle; if too small, it will run incessantly. Either way, it will not be energy efficient. Horizon recommends closed loop heating equipment where the combustion air intake is from the outside via a PVC pipe. The exhaust is also directed outside through a pipe. This sealed type of system will not allow for back drafting of CO and other flue gasses into the indoor air. We have also installed a multitude of geothermal systems. These systems must be used in conjunction with a ‘perfect’ insulation and envelope system or their high overall installation and operation costs will make them a bad investment. As an aside, geothermal systems are not a panacea in an attempt to save energy or CO2 emissions. They must be installed only when the building envelope is tight. The HVAC system must be thoroughly discussed prior to its final design. But whether you decide on geothermal or not, Horizon can help you specify the proper HVAC solution for your project.

EER, SEER – Energy Efficiency Ratio:
EER/SEER refers to the "Energy Efficiency Ratio" and is a number which indicates the equipment's energy consumption. It relates to the watts of electricity needed to move heat. Simply, the higher the EER the better the equipment. Equipment known as builder grade was once in the 8-10 EER range. The minimum now is 13, per law. An EER rating of 15 or above demands the equipment have electronically commutated motors. This is a much better system, but it also includes a higher price tag. You should insist on 15 EER or above for any home design project.

EER ratings in the 21-24 range are possible using standard split systems (AC units outside) and up to 43-45 using high end Geothermal systems. The old adage “You Get What You Pay For” is especially true in this case.

Ventilation, Dehumidification, Humidification, Filtration and Duct tightness:
Did you know the ‘code’ does not require controlled and deliberate ventilation. Typically your home inside air is 2.5-5 times dirtier or more polluted than the outside air. Most builders give lip service to ventilation. They say the house is tight and expect the bath and kitchen fans to ventilate. In reality, the house just leaks uncontrollably. This allows for a ventilation system of sorts. It also allows heat to invade and escape at uncontrolled rates. This is simply not energy efficient. As part of the overall ‘system’ Horizon provides for a controlled ventilation system, but there are multiple ways to design one. There are ERV’s, HRV’s and other systems.

Is controlled ventilation important? Yes, it removes and dilutes contaminants; it is what makes air healthy. Horizon can help you specify what’s best for your clients.

Dehumidification:
We typically specify and install a stand-alone specialty dehumidification system. It removes moisture from the air on days when the A/C system is called upon infrequently. It also levels the R.H. throughout the house and assists the A/C in removing moisture and lowering the temperature. It makes the A/C more effective and efficient and really saves money by affectively making the home feel cooler.

Humidification:
Nortec is the best humidification unit available today. It works well, adds comfort throughout the dry winter months and is easily maintained. That said, it is expensive, but you get what you pay for. If your client is concerned about dry air during the cooler months, it’s a good investment in comfort and protecting fine furniture and other woodwork.

Duct Tightness:
The supply and return duct will be sealed with water borne mastic at all the joints. This sealing keeps the air where it belongs. It keeps it in the conditioned ‘envelope’ space. This is a critical part of the overall system given it enhances air quality and energy efficiency. Also, the entire return duct will be metal - no ‘panning’ off of the joist bays is allowed.

We test the duct for air leakage prior to close in. If it leaks - we find it and eliminate it.

Filtration:
Filtration is used in conjunction with the other parts of the system to insure the air is healthy and comfortable to breath. It cannot be used as a substitute for ventilation. Typically HB installs thick pleated, media air filters. They work very well and in fact are more effective than electronic air cleaners. Stand-alone HEPA units can be added for special cases. A house, when constructed as a system, will not leak air through the interstitial spaces and will be much less dusty than is usually the case with traditional home construction. And regarding UV lights to prevent the growth of mold, etc., in air ducts, these systems do nothing to filter allergens such as pollen out of the air and have little or no affect on improving the quality of circulating air.

And Finally...Testing - Verification:
Horizon has developed a testing and verification protocol that expands on the National ‘HERS’ system, EPA’s Energy Star program and the DOE’s Builders Challenge program. Most programs require inspection and verification of air barriers, insulation and duct/HVAC systems during the process with ‘Duct Blasting’ and blower door testing held to near the end of the project. ‘Blower Door’ testing requires a knowledgeable and certified technician, specialty equipment and computer programs to analyze leakage, air exchange rates, etc. Horizon has, on staff BPI (Building Performance Institute) and HERS (Home Energy Rating Systems) certified raters. To become a BPI inspector and HERS rater demands multiple classes in building science, testing and mentoring. It is a real commitment in time and energy.

Horizon does blower door testing at the following stages:

• House air and water barrier 100% installed; windows, doors and roof installed. We test the envelope for leaks.
• Insulation installed, all duct installed - just prior to drywall. We test the tightness of the envelope, insulation and duct systems. We find leaks, if any, and eliminate them. Windows and doors are adjusted for optimum seal. The testing goes on as long as it takes to remedy any issues.
• Final tests - near the end of the project. This is verified and certified to be sure the home is sealed and tight.