#hvacinstall Archives - United CoolAir

August 30, 2019 by Matt Hanson

What is a Heat Pump and how does it work?

A heat pump represents a growing segment of the HVAC industry. In practical terms, it is a reversal of how the air conditioning system works. While air conditioners are used to cool air; a heat pump can be used to cool or heat the air. This is especially true conditions are in place for this use. Therefore, it is necessary to employ a heat pump where temperatures are more moderate. The Summer months of the mid-south area of the United States contains the ideal conditions for this type of system. Conversely, they can be converted into a heating application when the temps are a bit cooler. In areas such as Florida or California where temperatures are mostly warm, it is best to use an air conditioner only.

The Heat Pump Refrigeration Cycle

Heat pumps use a reverse refrigeration cycle as opposed to the regular vapor compression cycle of an ac unit. Heat pumps use the condenser section to generate heat whereas an air conditioner uses it to reject heat. A heat pump uses a small amount of energy to move heat from one location to another. In a similar way it can cool a building or office space by working in reverse.

Air conditioners and heat pumps work in a very similar way. The biggest advantage to a heat pump is to negate the unit handling the separate loads of heating and cooling. Since the heat pump is only transferring heat it can operate by electricity. Additionally, the unit does not rely on the burning of fuel to accomplish the process.

In the cooler months, a reversing valve reroutes the refrigerant path making the outdoor condensing coil function as the evaporator. In a likewise manner the indoor coil serves as the condenser. The evaporator absorbs the outdoor heat and is in turn used by the condenser to heat the indoor space. However, there is one remaining problem. The outdoor evaporator absorbs heat and must operate at temperatures lower than the outside air. This low operating temperature causes ice to build-up on the outside of the evaporator. Finally, auxiliary heat is used during the defrost cycle to provide indoor heat during this stage.

February 27, 2019 by Matt Hanson

Choosing a Dedicated Outdoor Air System (DOAS)

In order to comply with current strict ventilation standards in the HVAC industry, manufacturers’ are introducing innovative new equipment to improve indoor air quality. Dedicated outdoor air systems (DOAS) are one such methods used to help regulate temperature and humidity. Schools, hospitals, offices, and other commercial spaces can all benefit from a DOAS unit. As these systems become more popular throughout the USA and Canada, technicians and end users need to understand the operation and importance of these units.

Although DOAS units are not the primary source of cooling, they help the main HVAC unit work more efficiently. These units function by bringing in fresh air independently of other cooling and heating equipment. This pretreated air will ultimately save fan energy on the main HVAC unit and improve the overall indoor air quality. These units can be air-cooled, water-cooled and chilled water and may include variable capacity compressors.

How to Get Started

Specifying a DOAS unit usually begins with selection software. This takes the basic parameters of the installation and focuses on the specific needs and requirements for fresh air. The software will calculate the performance expectations and recommend additional modifications to the basic package. A variety of fresh air units handle a range of CFM and tonnage and include options such as water-source heat pumps and modulating hot gas reheat.

Other fresh air units could include direct expansion with an energy recovery enthalpy wheel. The unit should be able to handle the large latent ventilation load and deliver “neutral” air of 72°F to 75°F @ 50% RH. By separating the sensible load from the latent load, the unit will remove moisture from the primary source of fresh outside air. What this does is reduce the load on the primary AC unit that will be used in cooling the space. Ultimately, this leads to greater efficiency and better indoor air quality with a lower overall cost.

Why Install Equipment Indoor?

Many HVAC manufacturers provide outdoor rooftop equipment as DOAS units, but occasionally a customer might require an all indoor packaged unit. This is the case when the building topography does not allow for outside mounting. Furthermore, codes that affect historic buildings often don’t allow for HVAC equipment to be installed outdoors. This is the case even if there were ample room on the roof or outside. The indoor packaged solution typically realizes a smaller footprint. This aides in new installations as well as for retrofitting as part of a VRF or conventional DX air conditioning project.

Ideally, the performance of your DOAS unit should meet or surpass the ASHRAE 90.1 standards of ISMRE 11.1 and ISCOP 8.0 and adhere to a sound rating of less than NC-40. Dedicated Outdoor Units also include options such as the installation of MERV 8 or 13 filters. Units can also include special coil coatings to prevent rust and corrosion when installed in harsh conditions. Some examples would include Marine or paper mill applications. Lastly, units may also include a manual on/off override switch and meet the power requirements of 208/230 single or three phase or 460/3 phase power.

When calculating the need for a DOAS unit it is important to understand all the benefits.

By removing outdoor contaminants before they enter the building the indoor air quality will be greatly improved. Additionally, this will allow the main cooling unit to run more efficiently.
The dehumidification process removes moisture from the entering air which helps prevent the formation of mold. These elements can negatively affect the health of the building occupants.
Energy savings are also achieved by separating the ventilation requirement from the main cooling or heating unit.

Dedicated Outdoor Air Systems have become an integral component to an overall approach to HVAC installation. As concerns about climate change drive governments to enact more stringent energy requirements in the manufacturing process; DOAS units will continue to grow in importance. Ongoing developments will ensure that these types of units will become even more efficient and used well into the future.