Tag Archives: testing

The Air Conditioning will not cool the 2nd floor

In a two level home, hot air will rise to the highest point making the upper floors warmer in the summer than the rest of the house. The upper rooms are the often the furthest point away from the air supply which requires larger ducts to compensate for the distance and if the duct work is not properly sealed, any air loss if noticed first at the point farthest away from the fan.  In some cases, the builder in trying to avoid having bulkheads on the 1st floor will squeeze the duct work into a wall cavity which can choke of the air supply.

Image of a AC system used in residential housing
Typical split AC system

If there is access to the main duct work, have a look at the joints and branch connections for duct sealant or foil tape to reduce air loss. Sealing up these connections can really improve air flow at the end of the long duct runs.   If the duct work is new, then it is fairly easy to tape the joints with aluminum foil tape or apply a duct sealant. If it is an existing system then you need to clean the duct of the joints first before apply sealant.   Cloth duct tape work too, but does not stand up well when used on heating systems.

There may be balancing dampers on the branch line of the ducts which can be used to reduce air flow to the lower floors and force more air to the upper floors. Be careful not to close off too much air or the AC will freeze up. The supply air grill is the rooms can be used to adjust the air as well. The cheap plastic floor registers have little slider to control the air flow that slide open or close. These can be difficult to try and balance air flow with but will work as an On/Off control.   A better floor grill will have an opposed blade damper below the diffuser that can be used to reduce air flow.

Poor return air flow is another common problem.   Make sure the is a clean pleated style air filter installed and do not use 1” wide high efficiency filters, these just choke off the air supply.  A 4” wide high efficiency filter works great by having a much larger surface area that cleans the air and still allows proper air flow.

image of a partially frozen AC evaporator
Partially Frozen

If you can remove the filter while the fan is running, try to slide the filter out a few inches and let go. If it gets sucked back into the filter rack it can indicate a strong negative pressure in the return air duct.

Another common is issue freezing of the evaporator coil. A partially frozen coil will choke of the air flow. Leave the AC off for a few hours with just the fan running and then turn the AC on. Let it run for 15 minutes and check the temperature of the air supply. It should be above 50°F or 10°C, any lower and the evaporator coil can form ice. The ice can slowly build up and reduce air flow.

These are a few of simple steps that DIYer can do but never attempt to modify the control, electrical, piping, sheet metal or refrigerant of any AC system, call a qualified technician for service.

If all else fails, read the instructions

Buildings have always been changing, new material, new techniques and improved environments, that are slowly evolving to meet our needs.  In the past 10 years, the push to reduce greenhouse gases has accelerated this rate of change. In BC, the LEED standards mandated by municipalities, and the recently adopted ASHRAE 90.1-2010, are bringing some of the biggest changes in construction since the invention of Air Conditioning or the Elevator.  Most of these changes have also increased the complexity of the structure, and with any complex system, comes the increased probability of failure. Whistler

Take for example, this major high end hotel in Whistler. In the first two years, the owners of this property paid out over $100,000 in repairs because of problems with the mechanical system, that was not properly commissioned.  I was called to this site, to look at an issue with a make-up air unit ( MUA ) which was locking out on flame failure. On inspection, I noticed air blowing out of a sealed combustion chamber when the supply fan was on. This air pressure, was interfering with the burner ignition and causing the lock out. If the unit was 20 years old, this kind of issue can be expected, but this unit was only two years old. When I looked at the heat exchanger, the top part looked fairly new, while the bottom was a very dark colour. The duct work that was attached to this unit, looked normal and large enough to do the job.  However, how it had been connected, was a problem. The air flow over the heat exchanger was not even, it was creating a dead space over the bottom section of the heat exchanger. This difference, created thermal stress that warped the heat exchanger, just enough, to bend the tubes and open the seams. The manufacturer installation manual, did, provide proper instruction for the duct connection and, detailed the need for even air flow.  Although, due to how it was connected, it is highly unlikely the installer ever read the instruction. And so, I say thus, “When all else fails, read the instructions!”

 

Eng Air Make Up Air Unit
Eng Air Make Up Air Unit

The MUA, is used to pressurize the hallways and supply ventilation air to the building with outdoor air. Gas heating is used to warm the air in the winter and a chilled water coil is used for cooling the air in summer. A fairly common configuration for this type of building, but, there was also something unusual about how the chilled water was piped in. The Mechanical engineer, wanted to improve the efficiency, and use the cooling coil in the MUA, as an economizer, to cool the chilled water supply, when conditions allowed. This would reduce compressor operation and save energy. The design used a 3 way valve, to bypass the chiller barrel, and send the water to the MUA for cooling, instead of flowing to the chiller for mechanical cooling. When the economizer could not be unused, the compressor would cool the water and then flow to the MUA if the air required cooling. It would have worked too except for one little issue.

The mechanical drawing showed a 3 way valve, or at least that is what it tried to show. The symbol used for the valve on the drawing was a little unusual and was not very clear. The scale on the icon, may have been wrong when it printed and may have looked normal on a screen, but when printed, it did not come out right. There are a lot of little details in 2 dimensional mechanical drawings, and some can be confusing. I was told the plumber thought it was a thermometer and not a 3 way valve, so he  installed a tee instead, with a thermometer next to it. The construction plumber has no expertise in a Chilled water design, their skill is running piping. This little mistake, eventually resulted in a failed compressor, in the first 2 years, on a large chiller and, after the warranty and, long after the contractors hold backs were paid.

So why did two major pieces of equipment fail within two years?

Did someone forget to test the equipment? Did anyone inspect the workmanship? Who should pay for it? This is when the litigation phase of construction starts.

Had a Commissioning Authority been included on the design team, these problems would have been detected.