Small Tonnage Chiller (STC)

Small Tonnage Chillers (STCs) are one part of an overall heating, ventilation, and air conditioning (HVAC) system.

STCs produce chilled water (or glycol) by cooling the chilled water loop.

All STCs need a chilled water pump to move chilled water through their pipes. For some models, manufacturers offer a chilled water pump kit as part of the total package so that the customer need not buy
one separately.

STCs chill their water (or glycol) and reject the heat removed via one of two methods…

• Air cooled condensers
• Water cooled condensers

Although it will have a higher install cost, a chilled water system can often produce a healthier, more pleasant indoor environment than a packaged rooftop unit or DX split system because it offers…

• Better humidity control
• Better temperature control
• Better air quality
• Less ducted noise in the conditioned space

Outdoor Units

The outdoor unit transfers the heat from inside the building to the outside air.

To do this, the outdoor unit contains a...

1. Condenser- transfers the heat absorbed by the refrigerant in the evaporator to the outside air. As the condenser rejects heat, the refrigerant vapor condenses back to a warm temperature liquid before entering the expansion device and evaporator.
2. Compressor- circulates the refrigerant through the refrigeration circuit. It draws low-pressure refrigerant through the connecting pipes from the evaporator inside the building, then discharges it as high-pressure refrigerant to the outdoor condenser. The outdoor unit can serve two conventional air-handling units, or may be tied in with a full featured air-handling unit.
3. Fan- pulls air through the condenser coil, transferring heat from the condenser coil to the outside air. The use of a fan increases the efficiency of the coil without increasing its size.
4. Connecting pipes- two pipes connect the outdoor refrigeration unit to the indoor unit. The suction pipe is larger and insulated. The liquid pipe is smaller.

"Splitable" Packaged Units

Although most units ship as a factory charged, unitized package, 4-15 ton, horizontal, air cooled units can be field split. The condenser section can be placed close to the outside wall and the evaporator and blower installed near the conditioning zone. Installation is possible through standard height doorways and elevators. Refrigerant piping above the ceiling takes up less space than ductwork.

• 4-10 ton units have valves to shut off the refrigerant so that the unit can be separated.
• 12 and 15 ton units ship in two pieces.
• 5-15 ton, horizontal, water cooled units also can be separated to facilitate
  moving the units through doorways and up into the ceiling location.
• Premium units can be split due to their modular construction.

Inside an Indoor package unit

Indoor packaged units offer a low profile indoor design that eliminates the need for any unsightly exterior equipment.

Floor-by-floor installation provides independent zone and temperature control, eliminating many of the complications encountered with rooftop equipment.

Basic components inside an indoor package include…

1. Cabinet
2. Compressors
3. Condenser coil
4. Evaporator coil
5. Fans
6. Filter
7. Controls

Heat Pumps

Climates with moderate heating needs often turn to heat pumps as an energy efficient option for indoor packaged unit cooling.

Heat pumps use electricity and extract heat from the cool outdoor air, moving it into the indoor space to make it warmer.

The refrigeration circuit becomes a heat pump by using a crossover reversing valve.

1. Outdoor Air Coil- Outdoor Air coil transfers refrigerant heat to the outside air during cooling

3. Crossover reversing valve- When the heating is required, the heat pump's crossover reversing valve switches the refrigerant flow. Thus, the roles of the evap and condenser are reversed.

4. Indoor Coil- extracts heat and transfers it to the refrigerant during cooling.

2. Outdoor Air Coil- extracts heat from the outside air transferring it to the refrigerant during heating

3. Crossover reversing valve- When the heating is required, the heat pump's crossover reversing valve switches the refrigerant flow. Thus, the roles of the evap and condenser are reversed.

5. Indoor Coil- transfers refrigerant heat to indoor air during heating

The Refrigeration Cycle

Air conditioners use a vapor compression, refrigeration cycle that transfers heat from a lower temperature source to a higher temperature heat sink.

Heat naturally flows from hot to cold, so work is required to move heat from cold to hot. The work is performed by a compressor driven by an electric motor.

The compressor changes pressure between two compartments in the air conditioner by pumping a refrigerant through a connecting loop.

A package refrigeration loop or circuit consists of a...

1. Compressor
2. Air cooled condenser coil
3. Thermal expansion valve
4. Evaporator coil
5. Return loop

Montreal Protocol

The Montreal Protocol established an international agreement to make a concerted effort to reduce emissions that deplete the ozone layer. Since many refrigerants have an effect on the ozone layer, this was a key piece of legislation for the HVAC community.

It was agreed that several refirgerants will be banned and others phased out. The goal was to move from chloroflorocarbons (CFCs) to hydrochoroflourocarbons (HCFCs) and ultimately Hydroflourocarbons (HFCs).

CFCs are no longer sold and cannot be recharged into systems. HCFCs are being phased out with the goal of having them gone by the year 2030.

ASHRAE

American Society of Heating, Refrigeration and Air-Conditioning Engineers

http://www.ashrae.org/

ASHRAE sets the standard for the majority of HVAC work. It is essentially the governing body that decides what best practices, standards and requirements will be adhered to.

It is important to makes sure all HVAC systems are in compliance with ASHRAE codes. Recently ASHRAE has passed several environmental laws that will be phased in to major commercial property.

Air Handlers

Air Handling Units (AHU) or Air Handlers are used to circulate air throughout a space. On the most basic level, an AHU consists of a fan, a motor, a heating/cooling coil and duct work to supply the air to the space.

In refrigeration, chilled water is typically supplied from a central plant to the cooling coil. The supply/return air will pass over the cooling coil and give up its heat to the chill water. The now-conditioned air will be pushed to the zone.

Energy Star Bench Mark

"The Benchmarking Law requires that owners of covered buildings benchmark their buildings no later than May 1, 2011, and every May 1 thereafter. Like city buildings, only buildings equipped with DEP automatic meter reading equipment for the entirety of the previous year are required to benchmark water."

May 2011 is right around the corner!

Bench marking your building is fairly easy, but you want to make sure you do it right. Register for a username for Portfolio Manager on the Energy Star website and begin uploading you site's data.

To get officially bench marked you will need a PE but you can begin the process now.

Spare Parts

I can't emphasize the value of spare parts. As a former property manager I no the difficulty of balancing being prepared and working with in a budget. In these difficult financial times there is obviously pressure on management to "trim the fat".

Spare parts are NOT fat!

Even a full service contract that includes replacement parts are not going to guarantee zero down time for critical systems. When it comes to optimum operating conditions, having key components of your system backed up by spare parts are is paramount.

While there will be an extra cost, you'll save on lead time when a problem arises. An evaluation of longer lead-time parts should be done as soon as any new system is in place. For older systems that do no have spare parts on hand, consider adding them too.

There is nothing worse than knowing that your plant could be operating perfectly with a replacement part, but that part is weeks or even months away from being delivered.

Greater, Greener NYC

The Greater Greener New York Initiative is a terrific opportunity for the HVAC community. Announced in 2007, the Greater, Greener New York is part of PlaNYC, a revolutionary declaration backed by Mayor Bloomberg.


PlaNYC sets forth a variety of environmentally conscious goals. The earliest of these actions involves an Energy Star benchmarking, for commercial buildings over 50,000 sqft, that is required by May 2011. The benchmark is easily filed for online and made public. Buildings will be required to record their energy ranking and make efforts to increase efficiency.

While energy efficiency has always been a goal for the HVAC community, the Greater, Greener New York Initiative and PlaNYC puts an even greater emphasis on it. Nearly all of NYC's hundreds of skyscrapers will be looking for creative ways to save energy. This can vary from lighting retrofits, to chiller optimization, to load-shedding. It's possible that new ways to monitor and save energy that have not yet even been implemented will come from these efforts. As a whole, the HVAC community will need to meet this challenge as one of the #1 goals moving forward.