For Fan Coil details and maintenance, see the separate page on Fan Coils
As part of the original intention to incorporate environmentally sustainable features in its buildings, CCH designed the HVAC system to include a ground-source heat pump, a passive solar and tight building envelope, zoned systems (for townhouses with basements), auxiliary electric heating coils (“Emergency Heat”), and controlled fresh air intakes and exhaust.
The ground-source heat pump in the common house mechanical room warms water for heating during winter and cools water for air conditioning during summer. The water flows from the central mechanical room to each unit’s distribution system, called a fan-coil, over which air is blown to heat or cool the rooms. There is also a back-up electric heating system in each unit, known as “Emergency Heat.”
Fresh air enters the living spaces through intakes equipped with special dampers. Fans in the bathroom and kitchen can be used for spot ventilation as necessary. A special, programmable device called an Airetrak controls bathroom fans. The Airetrak is programmed to run the bathroom fan periodically at a relatively low speed, thus ensuring a baseline amount of ventilation.
Filters (all units)
All 41 units have fan coils and all 41 units have filters. These must be inspected at least three times a year. Once they show considerable dust buildup they need to be replaced. Very high-density allergy filters will do a good job of filtering while also significantly reducing the cooling/heating efficiency of the fan coil. This is an unavoidable trade off. As of late 2005, the best available filter for our fan coil systems is the "3M Ultra Allergen" filter. It provides the best tradeoff between filter efficiency and air resistance. Standard-size filters can be purchased through many retail outlets. Custom-size filters (necessary for many of our units) are available by special order from several online retailers.
Seasons
Our heating and cooling system is designed to operate in heating mode during the winter, air conditioning mode during the summer, and “off” during the more temperate "shoulder" periods in the Spring and Fall. During the shoulder seasons when no water is being supplied, each unit is equipped with an “emergency” or “twilight” heat setting to supply heat for the occasional chilly evenings. Even though this electric “emergency” heat is more expensive per BTU (British Thermal Unit) than our ground source heat pump heat, we actually save money by being able to shut off our central system during shoulder seasons. Each change of season requires changing the position of the switch on the main thermostat in each unit and in common spaces. During the shoulder seasons, most of us can open our windows when we get too warm and run our bathroom fans at night. However, allergy sufferers may either choose to operate window air conditioners or request that the community lengthen the cooling season. (Bob Cowherd, 2009)
Pipe Insulation
The HVAC pipes deliver hot water (120ºF) in the heating season and chilled water (55ºF) in the cooling season. Pipe insulation helps to maintain these temperatures and reduce energy use. During the cooling season, if there is any air in contact with the hvac pipes, the pipes will "sweat" like a glass of iced tea out on the patio on a hot and muggy day. This is true even if there is a bit of air space between the pipe and the insulation. During the original construction of our units, the hvac pipe insulation was installed inconsistently. Small pockets of air in contact with the pipes can be tolerable if the water that condenses on the pipes on the hottest days is not enough to reach sheet rock finishes. Water damages sheet rock and results in most cases in mold growth (see "Mold"). However, even small areas of air in contact with a HVAC pipe can generate amounts of water condensation that must be addressed.
Operation of the HVAC in Apartments and Townhouses without Basements
Your apartment or townhouse is heated and cooled by a fan coil. The fan coil consists of a fan that circulates air throughout the apartment and through a coil containing warm or cold water provided by the central HVAC system. The fan coil also has an electric resistance coil (like a typical toaster) that can provide emergency heat (independent from the central HVAC system).
In apartments and townhouses without basements, the fan coil is located behind a large metal hatch in an area of the ceiling that is lower than normal. The lowered or "dropped" ceiling area contains most of the equipment, ductwork and piping that comprise the apartment's HVAC system. Townhouses and larger apartments will have larger fan coils and more extensive ductwork.
The airspace containing the fan coil (within the lowered ceiling area) is called the "return plenum." Air in the living space is pulled into the return plenum via a filter grille located near the fan coil unit (see "Filters," below). Fresh air also enters the return plenum via the fresh air intake. Inside the fresh air intake, a special device called a CAR (or Constant Air Regulator) limits the amount of incoming fresh air. In most units, a foam product called Icynene was used to seal the return plenum and prevent air from bypassing either the filter or the fresh air regulator.
Be advised that the boundary of a Unit extends to the true ceiling -- i.e. the ceiling that is above all of the HVAC equipment, not the lowered ceiling that conceals the equipment. You are responsible for any equipment that serves only your Unit, including ducts and piping that may extend beyond the physical boundaries of your Unit.
Regardless of size, a single thermostat controls all units. There are four functional settings on your thermostat. "Off" should be self-explanatory and in most units stops the fan. ) "Heat" is for routine warming of your unit. The maximum flow of warm air out of the ducts will never exceed 115-120 degrees F. Therefore the air at the duct feels merely warm, not hot, to your hand. The standard for most people’s comfort and for energy saving is around 68 to 70 degrees.
The "Heat" setting should only be used when the central heat pumps are creating the hot water to circulate through the system. The “Fan” setting can be used to circulate air without either heating or cooling it in the "shoulder" periods of spring and fall.
There is often a discrepancy between your setting, what the thermostat thermometer registers and what a more accurate room thermometer registers. It is advisable to have one good thermometer for monitoring. "Cooling" works when the central system has been switched to produce a flow of cold water to all units. A setting around 72 to 76 degrees will provide adequate cooling and dehumidification. Condensed water from the fan coil falls into a drip tray, which is connected (via two redundant pipes) to a nearby drain. The drain lines have the potential to block and cause minor but troublesome flooding. The lines should be inspected once yearly just to be on the safe side.
"Emergency Heat" can serve several useful functions. At the "shoulder" times of the year in spring and fall the central system may be shut down for energy conservation and to give the equipment a rest. Also, there may be emergency situations when the central machinery is shut down for repairs. Emergency heat consists of an electric heating element inside the fan coil. This will provide minimal heating, enough to keep you and your pipes from freezing. It will not keep you comfortable if the outside temperature is below freezing. The emergency setting can never be used in conjunction with standard heating or cooling.
Townhouses with Basements (a.k.a. "Home Run" systems, 101, 102, 103, 116, 117, 118, 120, 121)
These townhouses have large fan coil machinery in the basement (known as the Home Run Multi-Zone Distribution System). There are 9 zones individually controlled via room thermostats. There is one master thermostat on the first floor with the settings described above. In some houses the "off" position does not work, and only the circuit breaker can silence the whole operation. It may seem confusing, but actually, The “OFF” position is a "feature". In the "OFF" position, the thermostats behave as if the main thermostat was in the "HEAT" position. However, the water pump does not run, so there is no heating or cooling (theoretically, that is). This functions as a kind of "FAN ONLY" mode, where each thermostat can be used to control its associated fan.
On the Home Run control box, which is attached to the fan coil in the basement, there is a switch that can be set to "Home" or "Away". When set to "Home," the nine zone thermostats function independently, as they normally do. When set to "Away," the entire system is controlled by the Master Thermostat. Presumably, the intent of this design was to provide a manual setback for the purpose of saving energy when the home is unoccupied for long periods. For this purpose, it should be more effective - though perhaps less convenient, to reset each of the individual zone thermostats.
Note that the "Away" setting can be used in conjunction with the Master Thermostat to temporarily silence the entire system. An easier way to do this is to use the circuit breaker.
When Emergency Heat is on, the Master Thermostat controls the entire system. With the Home Run system, there is a control box on the basement unit that allows you to choose between using the individually controlled thermostats (setting = “Home”) or the one master thermostat (setting = “Away”). The master thermostat functions only when Emergency Heat is on..
The air filter is found in the base of the fan coil box. It is easy to slide out for periodic inspection and change. The condensing pump is on the floor next to the main box, and water exits through the plastic tubing. (If the condensing pump fails, the water puddles on your floor). Replacement condensation pumps can be purchased at hardware stores or home depot. Home run filters are 24"x25"
Be careful not to block the large return air opening in your dining room. The individual room thermostats adjust the local room temperature; the master thermostat controls the fan coil operation.
Noise
All machines make noise, and all flowing water in valved piping makes noise. The noise level varies considerably from one installation to another. Presently the sound level has been reduced to the best of our abilities. The most worrisome sound level would be silence when you are calling for heating or cooling. That would suggest your fan coil was not working. A dramatic change in the level of noise or grinding sounds suggests problems. If you get such a change you should turn off the system and call the management company, in case the problem may involve the commonly owned portion of the system. If the problem is with your unit's equipment, it is your responsibility to repair it and you are free to call your own HVAC repairperson.
In the 8 townhouses with Homerun units there are about 15 motor driven fans forcing air through the nine ducts. These motors have a limited life span. The end is signaled by a bearing type noise louder than usual or else the motor silently fails and no air is pushed. These motorized fan motors are replaceable, spares are kept in Coho and expertise is available for installation.
Operation of the Airetrak
The Airetrak controller is the rectangular button in your bathroom with a ventilation symbol on it. It is preprogrammed to run the fan at a low speed for 10-20 minutes each hour. When the fan runs, it exhausts stale air from the unit and pulls in other air to replace it - reasonably fresh air, we hope. The Airetrak's programmed cycle is an integral part of the ventilation system. It guarantees "baseline" ventilation (i.e. the minimum amount of ventilation that is thought to be healthy). When the Airetrak is running during its programmed cycle, it cannot be turned off.
If more intense ventilation is needed (e.g. if someone is taking a hot shower), press the Airetak's button. This runs the fan at full speed for 20 minutes or until the button is pressed again. When the full speed mode is deactivated, the Airetrak reverts to its programmed mode (low speed or off).
The Airetrak runs once every hour. It can be programmed to run for only five minutes each hour up to the entire hour, in which case the fan never turns off. It can also be turned off for certain hours. (The intent of this was to economize by not running the fan when nobody is expected to be at home.) The fan speed can be programmed. The lowest speed that successfully opens the fan's damper is the best speed to use. The Airetrak should not be entirely turned off, because it is the only way to consistently circulate fresh air in your unit when windows and doors are shut. To access the Airetrak programming controls, remove the switch plate. Complete programming directions can be found in the Cambridge Cohousing owner’s manual. Many readers have found the instructions very difficult to understand so you may seek assistance from a sprinkling of technically oriented fellow Cohousers.
(Bob Melvin and John Nelson, 2005)