Noise Control at Cultivation Facilities: An interview with Acentech

-Acentech presenting at Internoise 2018 on ‘Recent Experience with Cannabis Production Facility Noise’ on August 28th.


Anderson Porter Design works with many clients who are in the early stages of establishing their cannabis businesses. This allows us an insider’s perspective on some of the processes involved with obtaining a license, securing a location, and designing and building a cannabis-producing or dispensing facility. Over time, we’ve come to anticipate some of the many roadblocks that our clients encounter along the way. We hope that this series of blog posts, under the heading ‘Why is Cannabis a Good Neighbor,’ will not only prove useful to individuals or entities preparing to enter the legal cannabis market, but also to concerned citizens who may worry about the impact that a dispensary or cultivation facility would have on their community.

Last year, APD worked with a client who was locating their cultivation facility in an industrial park in a rural Massachusetts town. Early in the programming phase of our work we began to identify some of the major hurdles and milestones that would arise during the project. Each time a decision was made, the implications of that decision were examined and accounted for in the design and construction timelines. One of the biggest decisions that must be made early in the design of a cultivation facility is the selection of a mechanical system. For various reasons, we are seeing more and more large-scale Massachusetts cultivators employ chilled water systems instead of the traditional forced-air HVAC units (more on that later). Integral to these systems are large chillers which typically sit outside of the building on an equipment pad and tend to make a fair amount of noise.

In the case of this particular project, once the mechanical system was selected and preliminary equipment selections were reviewed to determine the size and placement of the equipment pad, we approached the landlord with our client to let them know about the exterior amenities being added. At this point the landlord pointed out the proximity of the neighbors, noting that a residential development had been recently constructed just up the hill from this industrial park, and it was possible that these neighbors may be concerned about the noise generated by the mechanical equipment. Enter Andy Carballeira, senior consultant at Acentech, an acoustical consulting firm that was brought onto the team almost immediately to help us, and our client, understand the intricacies of the noise that would be generated on their site and how best to mitigate it to keep their neighbors happy. Andy’s team was able to design a special sound barrier wall to prevent the noise from the mechanical equipment from reaching the neighboring houses.

We sat down with Andy to discuss the project and learn a little bit more about what acoustical engineers do and why their work matters to our clients in the cannabis industry:

APD: For those of us who aren’t sound engineers and know very little about acoustics, give us a breakdown, in layman’s terms. How sound is measured, what kind of noise levels are we talking about here, and how can you reduce noise levels so neighbors aren’t unhappy?

AC: That’s a great question. Noise engineering is such a niche and specialized field, and we want people to understand it better, to raise awareness to the general public that noise can create major issues. Noise is measured in decibels (dB), usually with a filter that models human hearing called A-weighting. When measured with this filter (which is the most common practice), we present noise levels in “dBA”.

For reference, a person whispering about 6” from your ear will produce a noise level of about 20 dBA. An idling semi-truck at about 10’ away would produce around 90 dBA. In quiet communities at least 5 miles from a major highway you may experience background sound levels around 20 – 30 dBA. The sound of crickets chirping falls within a 35 – 45 dBA range and is referred to as ‘indigenous sound.’

The noise level of a chiller is like that of a lawnmower. A high-capacity chiller might be closer to the noise level of a chainsaw. To measure sound pressure we really need to give a level as well as a distance – in other words as we walk away from a source it gets quieter. So, a chiller manufacturer will provide something called a “sound power level”. In much the same way that a light bulb may be labeled as 100 W, a “sound power level” is also expressed in watts, giving us an idea of the total ability of a piece of equipment to radiate sound out into the community.

When we’re analyzing sound, we use what we call the “source/path/receiver framework.” All three of these elements are relevant to our analysis. On the source side, we look to specify the quietest equipment. With the path, think of it like a line of sight – a sound barrier must prevent us from seeing the source in order to reduce noise transmission. For the receiver, we help to set the criteria by understanding the relevant limits on sound.

APD: When you’re designing sound walls to prevent unwanted noise from traveling to a receiver, what kind of regulations do you need to comply with?

AC: Here in Massachusetts, the Department of Environmental Protection (MassDEP) Noise Policy is our guiding document. It says that you must measure the existing conditions, and then you can add up to 10 dB on top of that existing level – this is true for all environments within the state of Massachusetts. The good thing about this policy is that one state policy works both within Boston and also out in Western Mass – it is measurable, and it addresses many different eventualities. We have a really good state policy, but some state or local policies may be vague, such as “if it sounds too loud to a person of reasonable sensibility”… This kind of interpretation creates a lot of risk for our clients. One of the first things that Acentech does on a project like this is to read every ordinance relevant to noise and understand actions that neighbors might take against a client based on noise. This is important – you have a right to know and understand the laws by which you are governed. In the case of this particular project, it was clear that the municipality wanted to refer to the state policy.  

APD: Can you tell us a little more about the state of the project when you were brought onto the team, and what your role and scope of work was?

AC: We had the opportunity to be involved early on – the site was selected, the location of the mechanical equipment was pretty well fixed, the overall mechanical design scheme was in a ‘DD (design development) phase.’  The design team had a sense of the required capacity for cooling and heating and knew where the equipment would go, but beyond that no noise study had been done and final equipment selections hadn’t been made.

APD had worked with the mechanical engineer to select the quietest equipment possible, and equipment that was capable of running at multiple speeds as capacity and requirements change so that the client could scale up and down based on needs and environmental conditions. It was up to us [Acentech] to say, with this fixed set of constraints, how to achieve a design that was in compliance with the MassDEP Noise Policy.

In order to do that, we did an analysis of the site, measuring sound levels both during the day and at night, and what we found presented some additional challenges. I mentioned earlier the ‘indigenous sound’ of crickets chirping – well, imagine the space in between the crickets chirping – that really quiet lull is similar to what we observed repeatedly on this site, with sound levels between 23 and 29 dBA. With these existing sound levels it was not unreasonable to say that the community was “whisper quiet”.

 [In case you didn’t already pick up on it, that means the facility equipment couldn’t produce sound levels over about 35 dBA at the nearest neighbors, which is still quieter than the sound of crickets chirping!]

Some of the nearest houses in the neighboring community are three-story structures situated as much as 70’ higher in elevation than the elevation of the equipment pad. Understanding the topography in 3D – building a model and placing the house and the equipment pad within that model so we could understand the sight lines from the upper story bedroom down to the different fans that are producing the noise on these chillers – that really drove the entire geometry of the system, from where the sound barrier went to what materials would be appropriate.  Part of the challenge was that we needed to be very careful with the sightlines [remember the ‘path’ part of the framework] because the worst outcome is that we build the sound barrier wall and get the geometry wrong. For that reason, our ability to work in 3D and work from GIS data was hugely helpful on this project.

APD: You mentioned the opportunity in joining the team early – why was this important? What might have been the implications had our client waited to install (or not installed) the sound wall your team designed?

AC: Sound barrier walls aren’t often considered during the planning stages of these facilities. This has been a significant problem for our one of our clients at another facility that opened recently in MA and didn’t study noise ahead of the fact; they also accepted an alternate on their chiller equipment. Between not looking at the potential impacts of noise and accepting this alternate equipment without understanding the way it would affect their operations, they ended up in a negative situation with the community.

        [In the case of APD’s client], the study by Acentech started at the end of the design process and overlapped the construction process. Construction had begun while the study was going on. What was clearly understood was that structurally the wall would necessitate foundations. For this reason, the optimal time to install the sound wall was during the construction of the slab – if it had come in after that was all in place there could have been additional cost implications for the client.

        One of the most valuable things we can do is be at the table when several sites are being considered, when we can say ‘Hey, I know this site has the amount of power that you need, but it’s right next to a senior citizen center’

APD: What advice would you give to our current or potential future clients who are looking to locate their cultivation facility?

AC: Well, a noisy site would actually be preferred because the regulatory limit would be higher since it is referenced to existing conditions.  Keep the noise factor in mind when visiting potential locations. Is the HVAC equipment to be located on the roof or at-grade? We are seeing lots of large chillers up on roofs with no noise mitigation. In this case, you’ve raised the source of the noise higher into the air so its ability to effectively broadcast sound over a wider area has gone up. In the project we’ve been discussing, we had to install a sound barrier wall, and had to counteract the wind and snow loads that the wall may experience. It wasn’t actually that tall, it was 12’, but to counteract the wind loads at grade we needed significant footings. If you were to do that on a rooftop, it couldn’t be done without modifications to the building structure. There are times (more and more frequently) where this is the case, and then you’re talking about moving the equipment off the roof or trying to stiffen the structure to accommodate the loads of these barrier walls. For a facility with rooftop equipment the expense can be prohibitive. You can end up in a situation where yes, there’s a solution, but it’s very costly.

 Most importantly, remember the source/path/receiver framework we discussed earlier. If you are able, use the building itself as a sound barrier wall between the noisy equipment and the receiver. Find receivers who are already in a loud environment. Be as far from the receiver as possible and select the quietest equipment possible. And of course, bring an acoustical engineer on board early to help you.

APD: Before we wrap up, we are conducting this interview as a part of an ongoing series entitled ‘Why is Cannabis a Good Neighbor’ … Why is noise mitigation particularly important to consider for cannabis facilities as opposed to any other industrial facility?

AC: Earlier I gave an example of another client we’d worked with who didn’t study noise impacts prior to opening their facility and found themselves in a negative situation with their host community. It’s up to the client to ask the questions of themselves and their team in the early stages: what is the downside implication to getting this wrong and having to shut down your operation? The cost of stopping your operation because of noise complaints is immeasurable compared to a line item you didn’t have in your budget when you were designing your project.

As our partner Brian Anderson also points out, it’s one thing to shut down an industrial operation and stop producing widgets for a day or two, but it’s immeasurably more costly to the cannabis industry when you’ve been working to keep these plants alive and preserve their genetics and make sure that they are all happy and healthy; the cost of shutting down the lights and HVAC systems for even one day could mean you lose all your crops.

We want to thank Acentech for partnering with us on this project, and Andy for his time and for sharing his knowledge with us (and with all of you!). If you are interested in learning more about acoustics and how they impact cannabis facilities, Andy recently presented a paper at the Internoise 2018 Conference – you can check out the white paper here. 

We hope these blog posts are helpful and informative – if you have a specific topic you would like us to cover please don’t hesitate to reach out to us either through our Contact Page or in the comments below. Thank you for reading!