Category: HVAC

In recent years, there has been a shift away from oversize HVAC systems that are simply too much for the space they need to heat and cool. This is because more emphasis in building and energy codes is towards energy efficiency. Buildings are required to have more accurate cooling and heating load calculations to prevent the problems associated with oversized systems. These problems can include short cycles and poor dehumidification, among other things. However, sometimes systems are still not sized correctly.

Things Are Heating Up

One of the problems that lead to oversized HVAC systems is that the installer used the incorrect design temperatures when making their load calculation. Here is how that happens. In the winter, heat bleeds from the building to the outside. In the summer, the building absorbs heat. How much heat is gained or lost, and how fast it heats or cools, is dependant on the difference in temperature from the outside to the inside. There is a table that provides the industry standard for the proper design temperatures for each season. However, too many contractors ignore or tweak those recommended temperatures when they are making their calculations.

Temperatures are always in flux, whether inside or outside a building. How much heat a building games or loses is in flux as well, even from hour to hour and day to day. If the goal is to keep the temperature of a building at a constant, such as 72 degrees, then the difference in temperature from outside and inside will be less in the evening and morning during the summer when it is cooler. When the temperature difference goes up, then the cooling load will have to rise as well. In most cases, buildings have air conditioners that are not designed to change the amount of cooling based on the change in temperature. THis would require split heat pumps, which are not common.

Design Temperatures

This is where design temperatures come in. Since most HVAC equipment is fixed capacity, and not variable, the design temperature will help make sure your system is operating at its best. The question is, what do these temperatures represent? In Winter, the 99% temperature refers to the level that the outdoor temperature will be above for 99% of the time. This is based on a 30-year average. This means that in the climate in which the building is located, the temperature will only be below that point for 1 % of the time. For example, in hotter cites, the 99% winter design temperature may be 25 degrees or so.

In the summer, the 1% design temperature is the point that your climate will be above for just 1% of the time. In a hot place, that point could be in the 80’s, for example. In the past, there used to be 97.5  and 2.5% temperatures. Those are no longer used since the current design temperatures have become the new standard.

Contactors and Design Temperatures

In general, contractors do not like having to return to the scene of a job to adjust things if the customer complains about being uncomfortable. This is why they will install oversized systems to make sure there is always enough cooling and heating. They do not know how about the other factors that come into play with the temperature of a building, such as insulation and infiltration. Despite this, if you are having a new system installed, make sure that the contractor uses the correct design temperatures so that you will not only be comfortable, but you can avoid any issues with having an oversized system for the space that you have.

Even with the best quality furnace or air conditioning system in the world, one needs a proper and effective duct work or else there will be loss of energy and money. This will cause the structure to have uncomfortable temperatures. Poor duct work will definitely affect negatively the quality of the air inside the rooms. Here are some essential facts on why tight ducts are effective for heating and cooling.

Importance of Tight Ducts for Effective Heating and Cooling.

Majority of structures in America are installed with forced air-heating and cooling system. A main heating, ventilating and air conditioning system mostly a heat pump, furnace or A/C which creates cool or warm air that is blown around by powerful fans through interconnected ducts and registers to reach the various destinations within the structure. This is a repetitive process where the ducts that supply air, take the heated or cooled air to the rooms, while return ducts and registers do the reverse by drawing the room air back into the equipment to be heated or cooled.

One would want to avoid defective ductwork, where ducts network is not well linked to each other, or to the registers, or to the furnace plenum.

Some negative causes of defective ducts.

Loss of energy, the HVAC equipment must operate above its required optimum in order to compensate for the lost energy as heated or cooled air is lost out into unconditioned areas such as the basement area , spaces below the roof , and even cracks on the wall . Some rooms never reach their optimum required temperature, because much of the conditioned air is lost through the faulty ducts before it even reaches the intended destination or room. This mostly affects rooms at the far end of a building whose ducts are long but leaking. Poor quality of air, this is caused by contamination of air from cracks and basement spaces that mix through the leaking points, this causes changes in the air pressure. The contaminated air is then circulated in the structure, lowering the quality of the air from the plenum.

How to Achieve Tight Ductwork.

The best way to achieve an air-tight duct is to hire a professional to do inspection of the existing network of ducts and seal the leaks with the necessary insulation. Although one may temporarily seal leaking ducts using sealants such as metal-backed tape or even mastic sealant in areas where the ducts are obviously leaking.