A client delaying payment

When a client tells me they will hear from the owner shortly and will pay me soon:

There is no calendar with a date called ‘shortly’, and there is no clock that has a time called ‘soon.’  Should I expect to get paid by the end of December 16, 2024?

Installing an air-cooled chiller with water side economizer, in the San Francisco Bay Area

 

 

September 20, 2022

I am designing a chiller plant for a client and wondering if I should have a water side economizer (free cooling module/dry cooler module) with the air cooled chiller I plan to use.  It is not an easy decision because I do not know what percentage of cooling (chilled water) will be used in air handling units.  If 100% of the chilled water will be used in air handling units then the water side economizer does not make any sense: when it is favorably cold outside, I'll just use the air side economizer of the air handling units and keep the chillers off duty.  If 100% of the chilled water will be used in the electronic racks then water side economizer makes perfect sense: I won't have any way to use cold air inside the building, but I can use turn off the chillers and just use the dry coolers to cool down the water, and then use the chilled water in the electronic racks. Installing integral free cooling modules with the air cooled chillers also makes sense if there is no provision for outside air at the chilled water coil units (Fan coil units or Computer Room units).  In these instances, there will be no way to use the cold outside air directly in the space but using the ambient cold air to cool down the water will be possible.

The problem I am facing is having no knowledge of the use of the chilled water in future.  The chilled water will probably be used mainly in the air handling units (say 60%) where air side economizer will be an option; probably 20% used in the fan coil units and computer room units where air side economizer is not present; and probably the rest (20%) will be directly used in the electronic racks to keep the processors cool.  With this distribution of chilled water capacity, it will be hard to justify the added cost of the water side economizers.

Photo: Courtesy of Trane.

Ductwork, a VAV box, pipes and lights hanging from the metal floor deck

 

Do you just need a fire damper or a combination fire smoke damper?

 

 You need just a fire damper when the barrier (wall, floor) is only a fire separation.  You need a combination fire-smoke damper when the barrier is both a fire and a smoke separation.  Who decides the nature of the barrier?  An architect or the City.
An actuator-driven damper gives you the flexibility to quickly bring back the damper to its normal (open position).
    The combination fire-smoke damper is actuated two different ways:
1.    Fire.  In case of a fire event, the high temperature is sensed by the sensor associated with the damper; a contact gets open, power to the actuator is cut off; the damper is closed.
2.    Smoke.  There is normally no smoke sensor being an integral part of the combination fire-smoke damper.  The signal of smoke detection must come from an external source (a duct-mounted smoke detector or a fire alarm panel).  The external signal is fed into the electronics of the damper.  When a signal is received, a contact gets open, power to the actuator is cut off; the damper is closed.

You don’t need a duct mounted combination fire-smoke damper in a fire-smoke separation barrier when the air moving system has a capacity of over 2000 CFM since such an air moving system is already required to have an automatic shut off based on smoke detection at the equipment level.

CAMC 608.1
“Air-moving systems supplying air in excess of 2,000 cubic feet per minute (944 L/s) to enclosed spaces within buildings shall be equipped with an automatic shutoff.  Automatic shutoff shall be accomplished by interrupting the power source of the air-moving equipment upon detection of smoke in the main supply-air duct served by such equipment.  Smoke detectors shall be labeled by an approved agency approved and listed by California State Fire Marshal for air duct installation and shall be installed in accordance with the manufacturer's approved installation instructions.....Where fire detection or alarm systems are provided for the building, the smoke detectors required by this section shall be supervised by such systems and installed in accordance with NFPA 72 and the California Building and Fire Codes.”

Photo courtesy of Ruskin

Tags: How does a combination fire-smoke damper operate?

Is there a smoke sensor in the combination fire-smoke damper?

A combination fire-smoke damper operated by a smoke detector.

A combination fire-smoke damper operated by a fire alarm panel.

Condensate drain line termination with Fan Coil Unit in the ceiling space/attic

 In inspecting buildings I often see how incorrect terminations of condensate drain lines, especially those that are coming from out-of-sight ceiling or attic-mounted forced air units/air handlers, causes a lot of problems (moisture in the walls, ceilings; mold).  The primary condensate line must connect with the drain line before a P-trap.  There should always be a secondary drain pan under the fan coil unit/air handling unit.  The drain line from the spill pan should terminate at a place where any water coming from there is in plain view and necessary action can be taken when that is the case.

In the photos below, the condensate drain line is connected to the sink drain and the secondary drain is terminated over the bathtub. 

Duct Smoke Detectors. Install in return, supply, or both return and supply air ducts?

Duct Smoke Detectors.

Install in return, supply, or both return and supply air ducts of an air handling unit?

Let’s first establish the goal of this exercise.  Why do we need duct smoke detectors?  The goal is not to fan the fire.  In case there is a fire, all air movement should be stopped so that the fire is not aided by the air provided by an air handling unit, a rooftop unit, a forced-air furnace, a supply air fan, or any other HVAC equipment.  A duct smoke detector is installed to sense smoke (a byproduct of fire), and in case there is a fire send a signal to an alarm panel so that the respective HVAC unit is shut down.

Now let’s imagine an HVAC system comprised of a rooftop unit. [The logic presented below applies to other HVAC systems comprising of supply and return air ducts.]

Scenario 1:  Duct smoke detector in the supply air duct.  Rooftop unit WITHOUT an economizer.

A)  If there is a fire in the space, the smoke will go in the return air duct, and ultimately end up in the supply air duct.  Once the duct smoke detector installed in the supply air duct senses the smoke, the signal will be sent to an alarm panel that will work towards shutting down the rooftop unit.

B)  If there is a fire in the rooftop unit, the duct smoke detector installed in the supply air duct will sense the smoke and other processes will follow to shut down the unit.

Conclusion: For units without an economizer a single duct smoke detector installed in the supply air duct will work fine.

Scenario 2:  Duct smoke detector in the return air duct.  Rooftop unit WITHOUT an economizer.

A)  If there is a fire in the space, the smoke will go in the return air duct where the detector will sense the smoke, the signal will be sent to an alarm panel that will work towards shutting down the rooftop unit.

B)  If there is a fire in the rooftop unit, the supply air will first go to the space, and eventually come back to the return air duct where the installed smoke detector will sense the smoke and other process will follow to shut down the unit.

Conclusion: For units without an economizer a single duct smoke detector installed in the return air duct will work fine too, but will expose the people to smoke in case there is a fire in the unit.

Scenario 3:  Duct smoke detector in the supply air duct.  Rooftop unit WITH an economizer.

A)  If there is a fire in the space, the smoke will go in the return air duct; if the unit is not running in the economizer mode it will ultimately end up in the supply air duct.  Once the duct smoke detector installed in the supply air duct senses the smoke, the signal will be sent to an alarm panel that will work towards shutting down of the rooftop unit.  BUT if the unit is running in the economizer mode, all return air will be exhausted, and the duct smoke detector will not have a knowledge of the smoke in the space.

B)  If there is a fire in the rooftop unit, the duct smoke detector installed in the supply air duct will sense the smoke and other process will follow to shut down the unit.

Conclusion: For units with an economizer a single duct smoke detector installed in the supply air duct will NOT work.

Scenario 4:  Duct smoke detector in the return air duct.  Rooftop unit WITH an economizer.

A)  If there is a fire in the space, the smoke will go in the return air duct where the detector will sense the smoke, the signal will be sent to an alarm panel that will work towards shutting down the rooftop unit.

B)  If there is a fire in the rooftop unit, the supply air will first go to the space, and eventually come back to the return air duct where the installed smoke detector will sense the smoke and other process will follow to shut down the unit.  But before this happens, people in the air conditioned space will be exposed to a lot of smoke.

Conclusion: For units with an economizer a single duct smoke detector installed in the return air duct will work, but it is better to have detectors in both supply and return air ducts to avoid exposing people to smoke.

 Photo courtesy: System Sensor

Revit vs AutoCAD

Revit is a powerful design tool. Revit begins where AutoCAD reaches in its stretches to reach in the 3-D domain.
In Revit you work in 3-D, right from the get go.

Collaborative Effort of the Design Team
In a design team, everybody works on their own Revit file.
For example, if you want to design electrical system for a building for which an architectural Revit file already exists, you will start from a new electrical template Revit file and then ‘link’ (pretty much like xref in AutoCAD) the arch Revit file.  You can then start working on your electrical design viewing the arch setup.
Revit families are like AutoCAD symbols, and Revit has extensive families.  Suppose you are working with the floor plan and say you want to show a transformer on your drawing, you will find transformers of different ratings in the transformer family. You drag and drop the transformer of your choice. As soon as you drop the transformer at a particular place in your drawing, the software
will ask you for the 'offset'--the third dimension (height) that you are currently not looking at in the floor plan.  In essence, all objects are placed in three dimensions and all views are coordinated.

Coordinated Views
If you are looking at an elevation view and change the place of a certain object, all views (floor plan, elevations, etc.) will automatically be upgraded to show the new location of the object you have moved.

Seeing Sections is a breeze in Revit
Revit makes it super easy to see sections.  In Revit, you DON'T make sections--they are already there, you have already drawn things in 3-D.
All you have to do is to drop the section line to see what a section across a space or object will look like.




Revit makes it easy to make schedules of material

If you are an architect
Every time you put a door on the drawing, Revit takes it into account.  When you opt for the door schedule all the information about doors you have used is automatically populated in the door schedule.

If you are an electrical engineer
Every time you put a transformer or distribution panel on the drawing, Revit takes it into account.  When you opt for the transformer or panel schedule all the information about the equipment you have used is automatically populated in the schedule.
The program even warns if you if a distribution panel is overloaded.

If you are a mechanical engineer
Every time you put an air device or a VAV box on the drawing, Revit takes it into account.  When you opt for the air devices or VAV box schedule all the information about the equipment you have used is automatically populated in the schedule.

The program even sums up the air flows, making you see if the sum of all air provided in a zone equals the air coming out of an air handling unit/FCU/VAV box serving that zone.

Out of sight, out of mind

Out of sight, out of mind

This exhaust fan serves a busy restaurant kitchen.
I sometimes wonder if there should be cameras focused on out-of-sight rooftop mechanical equipment.  If property managers will see this equipment more often, they will know its condition, and will be more inclined towards spending money for the upgrade work.

A roof full of rusted mechanical equipment

This site was close to the beach.  HVAC equipment appeared rusty before reaching its normal useful life.

Make shift arrangements

It is good to come up with innovative designs, but it is often more efficient and economical to buy products best suited for the application.

Variable speed fans in Packaged Units over 10 tons

Variable speed fans in Packaged Units over 10 tons

On a recent job I specified two 10-ton rooftop units.  The application was a Class 1000 Clean Room. I wanted constant volume rooftop AC units—initially, air handling units were discussed but because of budget constraints we had to settle for packaged units.  Later, when I reviewed the submittal that came from the contractor I did see the wording ‘Multi speed fan’ but did not get alarmed as many manufacturers provide units with low, medium, and high speed fan settings that is just a one-time adjustment at the start-up.  It turned out that because of the latest Title 24 mandates, all AC units over 10 tons now need to have varying speed fans.  The fan speed is varied based on the staging of the compressors.  In the old days, a ten ton unit will supply, say, 4000 CFM all the time, and the supply air temperature will be changing based on the staging compressors, but now the supply CFM will vary based on the staging of the compressors and the supply air temperature will remain almost constant.

This Department of Energy documents describes the changes meant to increase the efficiency of rooftop units:

http://www1.eere.energy.gov/buildings/technologies/pdfs/emrgtech11_shen_040313.pdf

In short, the AC units we received had variable speed fan motors.  Now the challenge was to change the fan to constant speed.  The first set of instructions from the manufacturer on changing the fan speed to constant did not work.  These were the instructions.

>>Unplug the J9 off the RTRM then unplug the J8 pins 6&7.  Reset power to unit and adjust the R136 to the desired fan speed.

The contractor kept talking to the engineering department of the manufacturer.  The second set of instructions did work.  Here is what worked:

>>For standard ID Fan operation, ensure RTRM 3J9, RTDM 5J12, and RTOM 5J8 Pins 6-7 are open (no connections).

I wish AC unit manufacturers will say it very clearly on their brochures: The supply fan speed is automatically varied based on the cooling requirements.  This is the default unit that will be shipped to you unless you specifically ask for a ‘Constant Speed Fan’ option.