It’s Not Always the Contractor’s Fault.

Although the time has come when warmer weather is upon us, the effects of this past winter are still being felt.  Recently, we were involved in an investigation that focused on the cause of damage to a water cooling coil located inside of a cooling tower (see photo below).  This might seem strange to some but, it is possible to require the cooling of a building during the winter.  In the investigation we were performing, the system was comprised of a water cooled water chiller.  This might not mean anything to most people but to those familiar with chiller operation, water was the fluid used to both cool the air and remove the heat absorbed by the refrigerant.  On the condenser side, water was circulated through a shell and tube heat exchanger and then pumped to another coil type heat exchanger located inside the cooling tower.  The problem arose when the local air temperature began to drop below freezing.  As the water temperature dropped below 40 F, water flow between the condenser and water coil was stopped (as part of the automatic control sequence).  As the air temperature continued to drop, the water temperature also dropped until the water froze inside the coil and caused it to burst in several places.  Since this was new construction, it was the engineer’s position that the mechanical contractor had erred and was negligent in their responsibility to protect the equipment.  However, it was later determined that the building had been turned over to the building owner under the substantial completion part of the contract.  As a result, the building owner was responsible for the protection of the building as well as the building’s mechanical systems.  Regardless of the positions taken by the various parties, the design of the HVAC system including the incorporation of freeze protection, was the responsibility of the mechanical engineer.  This responsibility is not an arbitrary assignment.  It has been long recognized by engineers and specifically, those engineers that are involved in HVAC design.  Although freeze protection had been designed into other parts of the system, no provision for freeze protection was made for the cooling coil located inside the cooling tower.  When all was said and done, the engineer failed to incorporate an adequate way to protect the coil and blamed the contractor in order to avoid the appearance of failure on their part.

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Destructive Force of Ice

As most everyone knows, this winter has been hard on just about every corner of the country.  It’s been a very cold winter and the southeast has had its share of low temperatures.  For this reason, buildings that must be protected against fire sometimes have to use dry sprinkler systems.  Conventional systems that pressurize lines with water up to the sprinkler heads are impractical because the lines are usually routed through areas (such as attics) that are subject to falling below freezing.  As a result, the water in the lines can freeze and cause the lines to beak or burst.  When thawing occurs, water damage will also occur.  In order to prevent such damage, dry systems are employed.  That is, instead of filing the lines with water, the lines are pressurized with air.  Pressurized air serves to keep the main water valve closed until such time as a fire causes the sprinkler heads to open and relieve the pressure.  As the air pressure is relieved, the main water valve opens, water fills the lines, and exits through the open sprinkler heads to fight the fire.  However, there are times when water can get into the branch lines.  Water can enter when there is a loss of air pressure due to a leak in the system or when water is completely removed such as after a hydrostatic test.  The photos below show what happens to an iron pipe tee when water is frozen inside.  In one instance, the tee is broken in half whereas in the second instance, the tee is fractured on one end.  Note that both fittings came from the same job.  Ice typically expands between 9 and 12% by volume and as a result, places a tremendous amount of pressure on the fitting walls to cause failure.

Air Conditioning in the Winter?

Whoever heard of air conditioning in the winter?  It’s cold outside and you need warm air, not cold to be comfortable, right? That certainly sounds reasonable.  After all, most people are using their furnaces at this time of  the year.  You might not be aware of it but, it is possible to create enough heat enough within an enclosure so as to require cooling instead of heating.  Most homes lose heat at a faster rate than can be replaced by supplemental sources (ovens, televisions, dryers, etc). As a result, some type of heating system has to be implemented in order to keep cold weather at bay.  However, in some office buildings, for example, the number of people and machines can easily produce enough heat to require space cooling in order to keep people comfortable.   Consider for example a 40 watt flourescent light bulb.  For each watt of power, the bulb produces 3.41 BTU/hr or 136.4 BTU/hr/bulb.  Most light fixtures are equipped with four bulbs. So, each fixture produces 545.6 BTU/hr. Imagine an office space equipped with 100 light fixtures. The total heat produced by all of  these fixtures is now at 54, 560 BTU/hr.  In terms of cooling, 1 ton of cooling is equal to 12,000 BTU/hr. The lights will require a cooling capacity of 4.5 tons. This doesn’t sound like  much but, when you start adding in other loads like people and computers, the heat output can be significant.

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