The Thermal Expansion Valve (TXV) is installed to control the flow of refrigerant into the evaporator in response to the cooling load. TXV’s measure the superheat at the outlet and react to this by increasing or decreasing the amount of refrigerant flowing into the evaporator to try and maintain a constant superheat.

Expansion valves reside between the evaporator and condenser in the refrigeration cycle. The main body of the TXV is made of brass with a refrigerator inlet on the bottom of the valve and a refrigerator outlet on the side. On the adjacent side is a cap that can be removed to adjust the superheat. Other components include a Power Head, Capillary tube and a Sensing Bulb usually made from stainless steel. The coil is stretched out so that that bulb sits at the exit of the evaporator to sense the superheat. The purpose of this is to ensure that the refrigerant is boiling off and this will leave the evaporator as a slightly superheated vapor and prevent liquid refrigerant entering the compressor. Liquids cannot be compressed because if they enter the compressor it can cause severe damage and even destroy the device. The bulb is filled with a separate refrigerant that is not mixed with the refrigerant in the rest of the system.

• The superheat boils the refrigerant inside the bulb and as it boils it creates pressure. The pressure travels along the hollow Capillary tube and into the Power Head and the Power Head controls the flow of refrigerant.
• A removable cartridge is placed inside the inlet of the expansion valve. This has an orifice, which works with the valve to control the refrigerant. There are different size cartridges depending on the cooling capacity needed and the type of refrigerant being used.
• The refrigerant comes from the condenser and enters the valve body through the inlet. It enters as a high-pressure, medium temperature saturated liquid. It then passes through the valve body and when it leaves, it exits the valve through the outlet and is converted to a low-pressure, low-temperature vapor/liquid mixture. This influences the pressure-temperature phase and controls the flow of refrigerant as the pin is connected to the diaphragm in the control head.
• The diaphragm is a thin sheet of metal that moves up and down with the pin. Underneath the diaphragm is a spring that can be adjusted to control the superheat. The sensing bulb sits at the outlet of the evaporator. As the cooling load of the evaporator increases the superheat increases at the evaporator outlet. Because the sensing bulb is in direct contact with the pipe of the evaporator outlet, the thermal energy transfers and causes the refrigerant inside the sensing bulb to expand and boil.
• As the refrigerant expands and boils it causes the pressure inside to increase. This pressure increases and makes its way through the capillary tube and travels to the chamber above the diaphragm. As the pressure increases it pushes down on the diaphragm and this pushes down on the pin. The pin controls how much refrigerant can flow and that is accomplished through an orifice assembly inside of the valve. The pin pushes down on the stop and the valve is opened. The more the stopper is pushed down the more the refrigerant can flow. As the cooling load increases on the evaporator, the superheat increases at the outlet.
• The sensing bulb at the outlet detects this and the refrigerant inside boils causing an increase in pressure along the capillary tube. This pressure pushes the diaphragm down which pushes the pin down which opens the valve and lets more refrigerant flow. As more refrigerant flows the superheat decreases so the pressure in the sensing bulb and capillary tube decreases which means there is less pressure pushing the diaphragm down. The spring then pushes the diaphragm back up which causes the pin to move up and as the pin rises the spring-loaded stopper begins to close the orifice which reduces the amount of refrigerant that can flow.

This repeats constantly and stabilizes the valve to ensure the correct amount of refrigerant can flow. The technician can adjust the amount of superheat by turning the adjuster left or right, which changes the sensitivity of the device and therefore allows you to tune the expansion valve and adjust the superheat.

Sick building syndrome sometimes referred to as tight building syndrome is a term that was developed from the ill effects building occupants incur because of poor indoor air quality. Although there is not one specific disease that is solely attributed to (SBS). Ill health and loss of employee productivity is a major concern of poor indoor air quality.

Chemical contaminant

Outside Sources: External air contaminants such as vehicle exhaust, ventilation ducts, and exhausts can enter the building through air vents, windows or by other means. Secondary combustible products can enter the building through nearby sources. Formaldehyde, radon, asbestos, dust and lead paint can enter the structure through various means.

Indoor Sources: The most common indoor air contaminants include volatile organic compounds (VOCs). The main sources of VOCs include carpets, tapestries, copiers, manufactured wood products, pesticides and cleaning agents. Environmental tobacco smoke, adhesives, breathable particles, combustion products from the stove, fireplace and unheated heater also increase chemical contamination.

Biological Contaminants

Biological contaminants include pollen, fungi molds, bacteria, and fungi. These bio-contaminants can grow in stagnant water that has been accumulated in humidifiers, drains or anywhere that moisture has infiltrated fabrics of insulation.

Bird and insect droppings is yet another source of bio-contamination. This type of pollutant can cause fever, chills, coughing, chest tightness, muscle aches, and allergic reactions. When workers are assembled in tight quarter’s airborne illnesses can be rapidly spread from one person to another. Air conditioning systems can further exacerbate the problem by recirculating the polluted air throughout the building.

Inadequate Ventilation

The oil embargo of 1973, pressed construction firms to create buildings more airtight, and with less ventilation to improve overall energy efficiency. The result has been that there is now less CFM per person in buildings than ventilation rates recommended by current ASHRAE 62.1-2016 standards.
Furthermore, the poor performance of existing HVAC units along with filters not being replaced as maintenance schedule recommends making the problem worse.

Electromagnetic Radiation

Microwaves, TVs, and computers emit electromagnetic radiation that ionizes the air. Electrical cables, without proper grounding, also create powerful magnetic fields that have been linked to cancer.

PREVENTION AND CONTROL

Today’s commercial buildings are designed and built with energy efficiency in mind. New construction techniques and materials used for the shell of the building minimize heat gains and losses and prevent the unwanted infiltration of moisture-laden outside air from entering the space, thereby decreasing the cost of space conditioning.
To maintain the latest ASHRAE ventilation requirements, owners/operators of commercial buildings generally have to depend on up-sized packaged rooftop HVAC systems not only to condition the recirculating air but to also bring in fresh OA to meet IAQ requirements. This results in larger equipment investments and higher operating costs.
A simpler, more effective solution is a 100% dedicated outside air system (DOAS) from United CoolAir Corporation working in conjunction with a sensible heating/cooling system. United CoolAir Corporation’s Alpha Aire, OmegaAir, and Modulaire 100% outside air units are stand-alone systems designed to meet the OA requirements for today and years to come. Traditional HVAC systems are designed primarily to handle design sensible loads and are not adequately designed for the high latent loads produced by outside air. The UCA DOAS units are designed to exclusively handle the large latent ventilation load and deliver “neutral” air of 72°F to 75°F @ 50% RH. DOAS units supply air dew point design temperature is lower than standard air conditioners to remove the maximum amount of moisture before delivery to the space.
By separating the sensible load from the latent load, the Outside air unit removes the moisture from its primary source—fresh outdoor ventilation air—at the lowest cost. Units can further assist the main space-conditioning unit by handling some of the smaller internally generated amounts of latent and sensible loads that naturally build from occupants and other sources. The result is better IAQ at a lower cost and healthier buildings.

Business owners in the market for a new or replacement commercial HVAC system are faced with many questions about where to start.  First and probably most importantly is the cost. However, cost not only pertains to the price of the equipment, one must also consider the installation cost. Equipment cost will vary from one brand to another and between companies performing the install. Since most buyers are usually not HVAC experts, they often defer to the expertise of the engineer or contractor and may not search or understand that there are alternatives.

Commercial HVAC systems are generally quite large and in many cases are installed when the building is constructed. The condenser unit is typically placed on the rooftop or outside the perimeter on the ground which causes them to be susceptible to weather damage and vandalism. The evaporator section is then placed in a mechanical room and cannot be easily relocated. These units generally need replaced after a few decades and the building owner is faced with the daunting task of choosing a replacement unit. Installers routinely tell building owners that in order to replace the unit, they will have to remove some of the walls or part of the roof in order to complete the retrofit install.  The reason is although the old unit can be chopped up and removed, it is very difficult to get a replacement unit in the space. Additionally, if the building is several stories high, a crane is needed to hoist the replacement unit into place.

The total cost of an installation can be broken down into separate categories; labor materials, and tasks. When it comes to labor, an install company will compute an hourly wage times how many laborers it will take to complete the change out. Other expenditures could include permits, insurance, supervision, warehouse, crane rental, and delivery. 

Other considerations that need to be made are the selection of the proper HVAC system. Owners, architects, engineers and contractors have the choice of chilled water, refrigerant direct expansion, packaged, air-cooled, water-cooled, and VRF systems. Will the system be a central or floor-by-floor method? Each of these will have pro and cons and can be one of the more difficult decisions to be made, and sometimes decisions are based on building codes.  If the structure is located in the historic district of a city, there could be restrictions of placing units out door or on the rooftop.

There is a better way!

United CoolAir  (UCA) products are designed to avoid all of the unnecessary costs that can occur in a typical retrofit installation. This is because; UCA HVAC units are designed differently than most other units on the market. It all begins with units that are designed as packaged systems and installed completely indoors. This factor alone saves the unit from weather damage and potential vandalism. Additionally, UCA units are built as modular units that fit through doorways, meaning there is never a need for expensive rigging or demolition of the building structure. UCA units can also fit into historic buildings thus avoiding the aggravation of code restrictions, additional permits or non-allowance for outdoor equipment. United CoolAir HVAC units not only save in installation cost but their units last longer over the competition.