I did not see any reference to my question and would appreciate a response as soon as possible, as due to medical situation, have to make a decision soon. We own an OLD house with 13′ ceilings in a large part of the home and 11″ ceilings in the LV/DR and BR. We are oscillating on where to place the ducts….Floor or ceiling. It appears to be counterproductive to me to put the duct work in the ceiling since it will have so far to go. We are looking for the most cost effective, not upfront cost but operating cost, solution. In addition, we are considering DF heat pumps. The house will need 2 or 3 to be zoned correctly. Please let me know about the duct placement and thank you for your help? Continue reading “Duct Work and High Ceilings” »
How many tons of air conditioning and heating do I need per square foot?
Rules of Thumb
It is not uncommon for HVAC estimators or HVAC contractors to use various rudimentary techniques which are generally referred to as rules of thumb. Some will say on the low end you need 1 ton of cooling for every 500 square feet. On the high end you will need 1 ton of cooling for every 700 square feet. These rules of thumb will also generally take into account a basic heat gain calculation for the kitchen and the number of people who will occupy the structure. At best these rules of thumb are educated guesses and may not give you an accurate calculation of what you really need. Unless the contractor used software based on the above mentioned manuals it would be to your advantage to actually do a proper load calculation for the structure based on Manual “J” or Manual “N” whichever is appropriate for your HVAC application.
Air Conditioner and Heating Ductwork
Manual “D” is used for sizing residential ductwork for the appropriate amount of airflow. For each ton of air conditioning you will need 400 cubic feet per minute (CFM) of airflow. It is imperative that this amount of airflow (400 CFM) be provided to the air conditioner evaporator coil of the air conditioning system. If the ductwork is too small it will restrict the amount of airflow crossing the air conditioner evaporator coil and this will likely cause big problems. If the ductwork is too big the system may have a problem generating enough static pressure to maintain designed airflow across the coil. The proper design and construction of the air conditioning and heating duct work is important for the proper functioning of the system. Using the proper techniques, software, and skilled personal will ensure that the HVAC job is accomplished correctly and will provide many years of reliable and efficient comfort to you.
Using good and time tested methods to size air conditioning and heating systems for your home or business is a smart thing to do. Using an HVAC estimator who is going to employ a rule of thumb for something that will be attached to your home and provide you with comfort for 15 to 20 years is not so smart. Use proper HVAC sizing methods and you will be better off and comfortable in the future.
Air Conditioning and Heating Sizing
The dampers straight across are outside air dampers or make-up air coming from an energy recovery unit. According to the mechanical code commercial buildings require a certain amount of fresh air from the outside to maintain good indoor air quality for the occupants. An energy recovery unit allows the air to be conditioned before being introduced into the building. Other methods include using enthalpy calculations to open economizer dampers and/or CO2 control of the dampers. The dampers at the bottom of the photo are the return air dampers. The return air will mix with the fresh air or outside air and go through the filters where the air is further conditioned based on what the control is calling for based on conditions inside the building, inside the duct work, and outside ambient air temperature. In HVAC using outside air can also be used for free cooling. Continue reading “Outside Air Dampers with Energy Recovery” »
The HVAC Air Handler Freeze Stat is a low temperature limit control and it is used mainly in commercial systems in the duct work on economizers or in air handlers just before any coil especially water coils. It is a safety and protection control to prevent extremely cold air from reaching the hot water or chilled water coils inside the air handler where the air enters from the economizer. Under ideal control set up if the freeze stat trips the economizer dampers close and the blower fan stops. This prevents coils from freezing. A frozen coil can bust open and will need to be replaced if it freezes thus the purpose of the freeze stat in HVAC air handler applications which utilize economizers for free cooling. Air Handler Freeze Stat
Vibration isolators protect the chilled water piping from receiving vibrations transmitted through the piping when the chillers are running. The vibrations can create problems not only for the chilled water piping but also for the buildings structure. The vibration isolators reduce or eliminate the vibrations that can be transmitted by the chillers. Other equipment normally specified with vibration isolators includes air handlers, pumps, condensing units, generators and most types of equipment with motors. Not only are vibration isolators required in the piping but vibration elimination springs or spring isolators are required are required on chillers, pumps, air handlers, and the other types of equipment named above which can produce vibrations when running. Vibration isolators are usually rated according to the static deflection the vibration isolator provides for the equipment. HVAC piping whether it is for hot water or chilled water usually is also specified with springs in the pipe hangers to avoid further issues that can be caused by vibration. Depending on the location vibration isolators will also be rated for seismic activity with further specifications calling for seismic restraints on the equipment and associated piping. Continue reading “Chilled Water Pipe Vibration Isolators” »
This is a direct digital controls control module for an air handler that serves some VAV boxes in office spaces for a Data Center. This DDC control module includes analog and digital inputs and analog and digital outputs to handle all the control functions necessary to control the devices and components on a large commercial air handler. Continue reading “DDC Control Module for an Air Handling Unit” »
HVAC Reznor Heating System LP Propane Gas Unit Heater – this Reznor unit heater provides heating for warehouses, garages, and other open spaces which can be heated with unit heaters. Unit heaters are ideal for big open areas which need heating without duct work being used to channel the air into the space. Sometimes these unit heaters are also used in mechanical rooms for protection of the other HVAC equipment and piping to prevent freezing conditions inside the mechanical rooms. The unit heater can be quickly installed and put into service in only a few hours once electrical service and gas service is provided in the location where the unit heater will be located. This unit heater is located in a remote camp site where electricity is available but natural gas was not available. LP or Liquefied Propane is trucked in to fill large LP Propane tanks located near the buildings which use these unit heaters to produce heat. A propane piping system and a series of propane gas regulators were installed and these unit heaters utilize the propane in the tanks being fed by this piping system. The regulators reduce the pressure from the tank to a usable pressure for the unit heater. Continue reading “HVAC Reznor Heating System – LP Gas Unit Heater” »
A good consideration when replacing the air conditioning system is the duct work. Duct work seems to be the most ignored part of an HVAC system but is a very important consideration in this age of new technology and higher energy efficient equipment being developed and manufactured. You can have the most energy efficient engine but if its in an old 60 or 70’s model car your efficiency is going to suffer. The same is true with HVAC systems. You can have the most energy efficient compressor available on the market but if your duct work is leaky or your house or business is not properly insulated that high efficient system you just spent big dollars on is wasted money. For more insight on HVAC ductwork see the High Performance HVAC Ductwork Page. Continue reading “Air Conditioner Ductwork Leaks” »
VAV Air Handlers are ideal for providing zones in a commercial building. Office space typically has several offices and open areas that need to be conditioned for the comfort of the people working in those areas or offices. By installing VAV boxes and zoning the duct work from those VAV boxes these areas and offices can be kept comfortable using a VAV air handler system. Each box can have its own thermostat and that area or office served by that particular VAV box can be maintained and conditioned for the people working in that space. The VAV box will receive its conditioned air from a VAV air handler through a primary duct that feeds air to the VAV box. The VAV box then determines the amount of air to the secondary duct by a damper located in the VAV box. Depending on what the thermostat temperature set point is and the temperature in the space will determine the amount of air flow the space will receive from the VAV box. Additionally, A VAV box with reheat will energize the heat strips or open the actuator for the hot water coil if the set point and room temperatures calls for the reheat to provide heat to the space (If the VAV box is equipped with reheat).
These filter banks filter the exhaust air from a welding lab where lots of smoke, fumes and related dust ends up going through these smoke filter banks. Specialized filtering systems are commonly used in industrial areas where fumes, smoke, and dust can be hazardous to the health of people working there. These are tied in to special exhaust fans and the buildings DDC system. Whenever someone enters a booth to begin welding in the welding booths they engage the smoke/fume exhaust switch and an exhaust fan energizes to pull any fumes and smoke out of the booth area and through the duct work where it terminates at these filter banks. The DDC monitors the differential pressure across the filters so when the filters are loaded up a signal is sent to an operator to change the filters. Specialized filter systems can be used for dust collection, smoke and fume collection and mitigation, gas vapors, and mist from liquids. Continue reading “Dust Smoke Filter Banks” »