Sunday, September 18, 2011

How to Charge An Air-Source Heat Pump In Winter

By Phil Rains
HVACRedu.net
About Phil!

Much interest has been shown in the correct requirements and/or procedures necessary for winter heat pump charging. The correct method(s) necessary for accomplishing winter charging are often included in an overall charging description, typically devoted to summer charging. In this article, we discuss only winter charging criteria.

Always remember that the ASHP (air-source heat pump) must contain the correct refrigerant charge to be able to transfer heat appropriately and meet the structure needs.

R410-A Refrigerant Charging

by Phil Rains

An R-410A air conditioner’s ability to operate as designed is dependent upon the amount of refrigerant it contains. U.S. Environmental Protection Agency (EPA) studies suggest that approximately 75 % of installed air conditioners possibly have incorrect refrigerant levels, which can reduce system capacity and efficiency by 20 percent or more.

Saturday, May 29, 2010

LADDER DIAGRAMS

By Roger Desrosiers
About Roger

Ladder diagrams are specialized schematics commonly used to document industrial control logic systems. They are called "ladder" diagrams because they resemble a ladder, with two vertical rails (supply power), and as many "rungs" (horizontal lines) as there are control circuits to represent. If we wanted to draw a simple ladder diagram showing a lamp that is controlled by a hand switch, it would look like this:



The "L1" and "L2" designations refer to the two poles of a 120 VAC supply, unless otherwise noted. L1 is the "hot" conductor, and L2 is the grounded ("neutral") conductor. These designations have nothing to do with inductors, just to make things confusing. The actual transformer or generator supplying power to this circuit is omitted for simplicity. In reality, the circuit looks something like this:



Proper Air Distribution and Air Flow

By Phil Rains
HVACRedu.net
About Phil!

Residential and light-commercial heating, ventilation and air-conditioning (HVAC) equipment distributes air throughout a residential and/or light-commercial structure by using an air distribution system. Designing a delivery system for air to flow in is critical. The proper operation of any heating or cooling system depends upon the duct design and layout. Poor design results in inadequate heating and/or cooling in some or all spaces in a structure. Poor heating and cooling is commonly attributable to insufficient equipment size even though the real problem is the conditioned air “delivery system”. When we say “delivery system,” we are actually talking about the duct work system (air distribution system).

If properly designed, the supply air and return air distribution is even and an approximate uniform temperature is maintained throughout the structure. Field studies have indicated that in some instances, the efficiency of air distribution (duct work) systems is over 50% less than it could be, because of poor design and leaks in the ducts. Many of these mistakes and problems can be corrected for little or no extra cost. However, proper air distribution can alleviate these problems from occurring in the first place, and if corrected after the fact, often increase savings for the occupant(s).

Sunday, May 9, 2010

Why Pre-Season Air Conditioning Checkups


By Roger Desrosiers
HVACRedu.net
About Roger

We all know the value of annual medical checkups because of the possible serious consequences that can develop, especially as we grow older. Finding a possible serious condition can save us a lot of grief. Well, this also applies to the possible consequences of not taking proper action in other aspects of our lives. One of which is the proper maintenance of our home/business air conditioning system.

Spring may not be a time when most of us are thinking about our air conditioning system, but it is the perfect time to schedule an annual check-up to make sure your whole home/ business is ready for summer. A pre-season check of your air conditioning system prior to the summer months can be a real money saver. When your air conditioner is running well it uses less energy to cool your house, and lower energy use means bigger savings for you on your monthly utility bills. Air conditioners at peak efficiency will use up to 20 percent less electricity and last years longer.

Sunday, May 2, 2010

R410-A Refrigerant Charging

By Phil Rains
HVACRedu.net
About Phil!

An R-410A air conditioner’s ability to operate as designed is dependent upon the amount of refrigerant it contains. U.S. Environmental Protection Agency (EPA) studies suggest that approximately 75 % of installed air conditioners possibly have incorrect refrigerant levels, which can reduce system capacity and efficiency by 20 percent or more.

The level of refrigerant charge is unique to each R-410A air conditioner and is determined by every component, including the outdoor coil and compressor, the indoor coil, and the refrigeration lines that carry the refrigerant between the coils. Correct refrigerant charge and proper refrigerant line sizing protect the compressor from damage, ensure efficiency, and improve performance. You should always verify the refrigerant charge for proper installation of an R - 410A air conditioner.

Sunday, April 18, 2010

Types of Split System Heat Pumps

By Roger Desrosiers
HVACRedu.net
About Roger


Two main types of split system air source heat pumps are; "All Electric" and "Add On". If a heat pump is added on to a fossil fuel furnace, the coil is installed in the supply air plenum, which is downstream of the heat exchanger with respect to air flow. It is therefore impossible to run both the heat pump and the backup heat simultaneously.

The mild 105 ºF heat from the indoor coil could certainly not be rejected into a 150 ºF air stream from the heat exchanger of the fossil fuel furnace. Therefore, anytime that supplemental heat is required, the heat pump must shut off and rest while the space is brought up to temperature by the more expensively fueled back up heat. This is why "add on" heat pumps are not as energy efficient as an all electric system.



Since the indoor coil of an "all electric heat pump" can be located upstream of the electric heating elements, there is no problem running the heat pump and the backup heating simultaneously. Note in the diagram how the RA (Return Air) is what enters the indoor coil, not the heated air from the electric elements.

Sunday, April 11, 2010

Residential Load Calculations

By Phil Rains
HVACRedu.net
About Phil!

A residential load calculation is a way for a contractor (or technician) to determine the envelope loads for a particular residential dwelling.

Every residential structure has these envelope loads which are determined by local weather patterns, features of the structure, and all the building materials and techniques that are or were used in its construction. Other parameters include appliances and the number of occupants in the structure, duct work loads, ventilation loads, and motor heat loads. Effectively, the envelope loads are the total heating and cooling loads for the components that surround the conditioned space (walls, ceilings, roofs, floors, doors, windows, etc.

The residential heating and cooling system must be selected and designed to provide comfort conditions in all occupied spaces regardless of whether is it winter or summer. The installed system must be able to control temperature, humidity, air movement and ventilation simultaneously.

Load calculations procedures produce improved equipment sizing loads for single-family detached homes, small multi-unit structures, condominiums, town houses and manufactured homes. These procedures are also compatible with different types of comfort systems and applications such as:

.Central single-zone systems
.Central multi-zone systems
.Distributed multi-zone systems
.Dwellings with limited exposure or no exposure diversity

Saturday, April 3, 2010

What Is Wet Bulb Temperature?

By Phil Rains
HVACRedu.net
About Phil!



“Wet Bulb temperature” is a term used by HVAC technicians when checking cooling operation with a “sling psychrometer”. The result indicates the temperature of air measured using a standard mercury-in-glass thermometer, with the thermometer bulb typically wrapped in gauze or a muslin-type material, with air passing over its surface. The covering is kept wet during testing. The evaporation of water from the thermometer has a cooling effect (Wet Bulb Depression), so the temperature shown is less than the temperature shown on a Dry Bulb thermometer used during the same test.

Saturday, March 27, 2010

OPERATION OF A VARIABLE FREQUENCY DRIVE CIRCUIT

By Roger Desrosiers
HVACRedu.net
About Roger

By the 1980s, AC motor drive technology became reliable and inexpensive enough to compete with traditional DC motor control. These variable-frequency drives (VFDs) accurately control the speed of standard AC induction or synchronous motors. With VFDs, speed control with full torque is achieved from "0" rpm through the maximum rated speed and, if required, above the rated speed at reduced torque. VFDs manipulate the frequency of their output by rectifying an incoming AC current into DC, and then using voltage pulse-width modulation to recreate an AC current and voltage output waveform. However, this frequency conversion process causes 2% to 3% loss as heat in the VFD — caloric energy that must be dissipated. The process also yields over-voltage spikes and harmonic current distortions.

Figure 1 shows a circuit diagram of a typical variable frequency drive. Notice how the circuit shows three separate sections. The first section shows the rectifier section, where a three-phase diode bridge rectifier changes the three phase AC voltage to pulsating DC voltage. The second section is the filter section where the pulsating DC voltage is smoothed to pure DC voltage. The third section is the transistor switching section which produces the three-phase AC voltage at the desired frequency.



Sunday, March 21, 2010

How to Charge An Air-Source Heat Pump In Winter

By Phil Rains
HVACRedu.net
About Phil!

Much interest has been shown in the correct requirements and/or procedures necessary for winter heat pump charging. The correct method(s) necessary for accomplishing winter charging are often included in an overall charging description, typically devoted to summer charging. In this article, we discuss only winter charging criteria.

Always remember that the ASHP (air-source heat pump) must contain the correct refrigerant charge to be able to transfer heat appropriately and meet the structure needs.

Saturday, March 6, 2010

INDOOR AIR POLLUTION

By Roger Desrosiers
HVACReducation.net
About Roger


What Causes Indoor Air Problems?

Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources, and by not carrying indoor air pollutants out of the home. High temperature and humidity levels can also increase concentrations of some pollutants.

Pollutant Sources


There are many sources of indoor air pollution in any home.

Saturday, February 13, 2010

PROPER TESTING OF HEATING EQUIPMENT


By Roger Desrosiers
HVACReducation.net


To ensure safe and efficient burner operation, all residential, commercial and industrial space and process heating equipment must be properly tested for:

. Carbon monoxide
. Smoke (Fuel oil only)
. Excess air
. Stack temperature
. Draft
. Possibly NOx, NO, NO2 and/or SO2

Saturday, January 23, 2010

Evaporative Condensers

By Roger Desrosiers
HVACReducation.net.

Evaporative condensers reject heat from refrigeration and air conditioning systems while using minimum quantities of energy and water. As shown in Figure 5A, water is pumped from the basin section and is distributed over the exterior of the condensing coil by a series of distribution troughs or spray nozzles.

Figure 5A

The flow rate of water need only be enough to thoroughly wet the condensing coil to provide uniform water distribution and prevent accumulation of scale. Therefore, minimum pumping horsepower is required.







A fan system forces air through the falling water and over the coil surface. A small portion of the water is evaporated, removing heat from the refrigerant, and condensing it inside the coil. Therefore, like the cooling tower, all of the heat rejection is by evaporation, thus saving about 95% of the water normally required by a "once-through" system.

The evaporative condenser essentially combines a cooling tower and a refrigerant condenser in one piece of equipment. It eliminates the sensible heat transfer step of the condenser water which is required in the cooling tower/refrigerant condenser system. This permits a condensing temperature substantially closer to design wet-bulb temperature, and consequently, minimum compressor energy input.

Saturday, January 9, 2010

What Is A Wet, Atmospheric Cooling Tower?

by Roger Desrosiers

A cooling tower is a heat rejection device, which extracts waste heat to the atmosphere though the cooling of a water stream to a lower temperature. The type of heat rejection in a cooling tower is termed "evaporative", in that it allows a small portion of the water being cooled to evaporate into a moving air stream to provide significant cooling to the rest of that water stream. The heat from the water stream transferred to the air stream raises the air's temperature and its relative humidity to 100%, and this air is discharged to the atmosphere. Evaporative heat rejection devices such as cooling towers are commonly used to provide significantly lower water temperatures than achievable with "air cooled" or "dry" heat rejection devices (like the radiator in a car), thereby achieving more cost-effective and energy efficient operation of systems in need of cooling. Think of the times you've seen something hot be rapidly cooled by putting water on it (which evaporates, cooling rapidly), such as an overheated car radiator. The cooling potential of a wet surface is much better than a dry one.

Friday, December 25, 2009

Gas Furnace Troubleshooting Tips

by Phil Rains

As technicians, during colder months you will be involved with troubleshooting gas furnaces that are not performing as expected or desired. There are several troubleshooting tips that will assist you in assuring the furnace works correctly. We will discuss a few of these in this article. Always follow the furnace installation and operation instructions.

First, you must assure that the furnace is the correct size for the structure heat loss load. This step is often overlooked since the furnace is already installed and not working correctly. But, you should make sure that the furnace is sized to provide 100 percent of the design heating load requirement plus any margin that occurs because of furnace model size capacity increments. Heating load estimates can be made using approved methods available from several sources like the Air Conditioning Contractors of America (Manual J). Most furnaces are of sufficient output capacity to meet most loads if installed by competent technicians, but, always determine if you have enough output capacity with the furnace you are troubleshooting to meet the structure heating needs. Also, excessive oversizing of the furnace could cause the furnace and/or vent to fail prematurely. Never oversize the furnace greater than 140% of the heat loss load.

Sunday, December 20, 2009

Capacitor Start – Capacitor Run Motor

by Roger Desrosiers

Capacitor Start-Capacitor Motors or (CSR) are used almost exclusively on Hermetic and Semi-Hermetic motors compressors. Rarely will this motor be used on an open type motor because of the cost of the components necessary to produce it. Most open–type motors do not use a starting relay, but use a centrifugal switch instead. Open type motors are usually built as permanent split-capacitor or capacitor start motors.

Operation

The CSR motor begins operation on a phase displacement between the start winding and the run winding, which allows rotation to begin. The run capacitor adds a small amount of starting torque but its main function is to increase the running efficiency of the motor. The run capacitor is wired in the circuit to provide the most efficient phase angle between the current and voltage when the motor is running. The run capacitor is in the circuit any time the motor is running. Both the start and run capacitors are wired in series with the start winding but are in parallel with each other. Figure 1 shows a schematic diagram of the motor with the starting components.



Sunday, December 13, 2009

Gas Furnace Start Up Tips

by Phil Rains

As technicians, during colder months you will be involved with the start up of gas furnaces for proper heating of homes. This will involve both visual inspections and effective start up procedures. We will discuss a few of these in this article.

Prior to the start-up of a gas furnace there are several things that you should verify. These are usually items that can be accomplished by visual inspection.

First, verify the type of fuel being utilized. As simple as this may sound, it is an important item to check. The furnace nameplate will typically detail the type of fuel that should be used. Almost all manufacturers today will produce furnaces that are set-up to use natural gas. These furnaces can easily be converted to LP gas operation by installing the correct LP conversion kit. Part of this kit may be a sticker or a new rating plate that identifies the converted furnace as an LP gas furnace.

Sunday, December 6, 2009

OIL PRESSURE CONTROL

by Roger Desrosiers

Many refrigeration compressors serviced today have positive-displacement oil pumps to help lubricate the internal compressor parts. Most compressors that have positive oil pumps also have a control that senses oil pressure and acts as a safety device whenever the oil pressure falls below a certain threshold level.


It is the action of the oil safety control we will discuss in this article.

There are several types of oil safety control devices on the market today. The two basic controls we are most familiar with are the mechanical differential control and the pressure-sensing electronic control.


The mechanical control uses tubing that senses the suction pressure of the compressor and the outlet oil pressure of the pump. The electronic control has a special pressure sensor that mounts in the outlet of the pump and connects only with an electrical cable.

Saturday, November 14, 2009

Troubleshooting a Non-Condensing Gas Furnace Pressure Switch

by Phil Rains

If you work in the HVACR business, you have probably had the opportunity to troubleshoot non-condensing gas furnaces in the field, whether packaged units, or furnaces combined with air conditioners or heat pumps (split systems). These furnaces are typically rated around 80% AFUE (a measure of efficiency), and are vented to the outside via a metal vent/pipe configuration, or in the case of a packaged system, a side discharge outlet/hood.

On occasion, the non-condensing furnace control board (called various names like integrated ignition control, furnace control board, DSI, etc.) has a diagnostic LED light, especially on modern furnaces. Abnormal heating operation can often be indicated by the diagnostic LED light on the control board if the unit encounters an internal fault.

Hi Efficiency Heating and Cooling Unit Operating Characteristics

by Roger Desrosiers



Blower Operation

1. The blower will operate continuously whenever the mode selector of the electronic thermostat is set in the cool mode and the fan selector is set to on.

2. The blower will operate intermittently whenever the mode selector is set to cool and the fan selector is set to auto. A delay is programmed into the microprocessor to allow the blower fan to continue to operate for one minute after the condensing unit has been commanded off by the thermostat.

3. The blower will operate intermittently whenever the mode selector of thermostat is set to heat. The fan is commanded on 35 seconds after the main burner lights and remains on for a predetermined time set by dip switches after the main burner is commanded off.

Heating Cycle

Sunday, November 1, 2009

HVAC/R Electronics # 6

by Roger Desrosiers

Improving air quality is another opportunity for engineers to apply the capabilities of digital systems. Energy conservation strategies require buildings to be airtight to prevent the escape of expensive heated or cooled air. This usually comes at the expense of ventilation. “Sick building syndrome” has become a national concern as researchers continue to uncover the effects of indoor air quality (IAQ) on human health and productivity in the workplace. Concerns over health hazards in the workplace and the spread of airborne contaminants are issues that have reached the forefront of public attention. The control of building ventilation is a problem that is being solved through the application of digital controls. So let’s take a look at a ventilation program.

Ventilating Control Program



Sequence of Operation:

Saturday, October 24, 2009

Air-Source Heat Pump (ASHP) Auxiliary-Supplemental Heat Sizing

by Phil Rains

Most ASHPs will have electric heaters installed within the “air handler” (where the supply air duct work originates). Outdoor temperatures lower than the structure “balance point” requires an additional heat source since the ASHP refrigeration cycle alone will not produce enough heat for indoor comfort needs during winter months. This additional heat is often called either auxiliary or supplemental heat.

Typically, around 30 - 40 degrees the ASHP will generally be able to produce the same amount of heat with the compressor and refrigerant cycle alone that the structure is losing (this is considered the structure "balance point”).Every structure has a distinctive “balance point” which can be calculated.

Monday, October 19, 2009

HVAC/R Electronics # 5-DDC Controls

by Roger Desrosiers

DDC control consists of microprocessor-based controllers with the control logic performed by software. Analog-to-Digital (A/D) converters transform analog values into digital signals that a microprocessor can use. Analog sensors can be resistance, voltage or current generators.

The microprocessor unit (MPU) in the controller provides the computation. Therefore, the term digital in DDC refers to digital processing of data and not that HVAC sensor inputs or control outputs from the controller are necessarily in digital format. Nearly all sensor inputs are analog and most output devices are also analog. In order to accept signals from these I/O devices, A/D and D/A converters are included in the microprocessor-based controller. The figure below shows several inputs and outputs. The microprocessor usually performs several control functions.

Saturday, October 10, 2009

R-410A Air Conditioner Refrigerant Charging

by Phil Rains

An R-410A air conditioner’s ability to operate as designed is dependent upon the amount of refrigerant it contains. U.S. Environmental Protection Agency (EPA) studies suggest that approximately 75 % of installed air conditioners possibly have incorrect refrigerant levels, which can reduce system capacity and efficiency by 20 percent or more.