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COVID Equipment: Low-Noise Strategies


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An overhead view of HVAC units on top of a building

As I am starting this blog I’m looking at my essentially silent lamp on my desk.

The main reason my lamp is so quiet is the actual source of electricity is far away from me, and there is no power generation happening at my lamp. There are plenty of noisy machines where the desired output is generated within the machine – like window air conditioning units, where the actual cooling is generated within the machine. And these are the noisiest kinds of machines – ones that generate their own electricity or their own cooling.

When I am asked to help a client with strategies to increase ventilation rates, all the more common now with COVID, I think about where to locate the new ventilation equipment based on the equipment’s noise level. I think about whether or not the machine is making its own cooling or electricity, or if it is relying on another machine far away for cooling or electricity.

With this in mind, HVAC and electrical equipment can be categorized in one of five groups by their primary use (meaning some equipment will fall under multiple categories). In order from (approximately) the noisiest to least noisy, these equipment categories are:

1. Equipment that makes its own power – like generators, making their own power and not relying on the grid

2. Equipment that makes its own cooling – like window air conditioners or packaged rooftop units, including their own refrigerant components like compressors and condensers. This equipment can also be a cooling source for other equipment. This equipment may still need to rely on other equipment to complete the cooling system, but there is cooling within the machine. 

3. Fan in a box – Blows air over coils to distribute cooling – the cold fluid is generated by another machine outside of this machine, likely from category 2

4. Damper in a box – Determines how much cold air is distributed into a room – the cold air is generated by another machine outside of this machine

5. Equipment that makes its own heating – Less equipment is needed for heating as compared to electricity or cooling

Equipment that falls under these categories includes:

1. Equipment that makes its own power

  • G: Generators

2. Equipment that makes its own cooling

  • ACCU: Air-cooled condensing unit
  • ACH: Air-cooled chiller
  • ACU: Air-conditioning unit
  • ADC: Adiabatic dry cooler
  • CH: Chiller
  • CT: Cooling tower
  • CU: Condensing unit
  • DC: Dry cooler
  • HP: Heat pump
  • PTAC: Packaged terminal air conditioning unit – packaged is the key word meaning the machine makes its own cooling
  • RTU: Packaged rooftop unit
  • VRF: Variable refrigerant flow – outdoor unit
  • WCH: Water-cooled chiller
  • WSHP: Water-source heat pump

3. Fan in a box

  • AHU: Air handling unit
  • DOAS: Dedicated Outside Air Unit
  • EF: Exhaust fan
  • ERU: Energy recovery unit – most do not make their own cooling (but some do)
  • ERV: Energy recovery ventilator – most do not make their own cooling (but some do)
  • FCU: Fan coil unit
  • FPB: Fan-powered box
  • FPT: Fan-powered terminal
  • MAU: Make-up air unit – most do not make their own cooling (but some do)
  • MUA: Make-up air unit – most do not make their own cooling (but some do)
  • P: Pumps – does not fit nicely in this category or other categories, but its noise output is a similar order to fan-in-box equipment and pumps also depend on other connected equipment – usually often in mechanical rooms, far from occupied spaces. And pumps are analogous to fans – but for water or another fluid instead of air.
  • SF: Supply fan
  • SPF: Stair pressurization fan
  • VRF: Variable refrigerant flow – indoor unit

4. Damper in a box

  • ACD: Automatic control damper
  • VAV: Variable air volume box

5. Equipment that makes its own heating

  • B: Boiler
  • Furnace: Typically part of a larger piece of equipment like a packaged rooftop unit

Other equipment allows noise to transfer through it to the rest of the building, if connected by piping to other noisy sources. For the most part, this equipment is not a noise source itself. This category of equipment includes:

  • AS: Air separator
  • BT: Buffer tank
  • ET: Expansion tank
  • FTR: Fin tube radiator
  • HX: Heat exchanger
  • RP: Radiant panel

Ultimately, a successful approach for low-noise strategies while increasing ventilation rates for COVID-related design solutions relies on traditional noise control methods. These include locating new and noisy equipment far away from occupied spaces, larger sized ductwork to reduce velocity noise, sound attenuators to reduce fan discharge noise, and locating volume dampers far away from diffusers. Simply turning an existing fan to a higher speed to deliver more airflow means that the fan is both less efficient and noisier – so while that might be a short-term solution to increase air exchange rates, it is not a great long-term approach either for energy consumption or for noise. Most importantly, make sure that equipment that makes its own cooling or its own electricity is far from occupied spaces, so that the radiated noise from the equipment is far from potentially sensitive listeners.