The cost of doing it right (dedicated MA unit) is nothing compared to the cost of forever having it wrong.

Just my opinion.

 

What is the downside?

 

I feel that I won't adequately describe the issues, but I will try.

One issue is that utilities expense will be significantly higher. The kitchen exhaust removes excess heat and humidity from the cooking area. That heat and humidity is simply a byproduct of cooking. However, by using an economizer you will be exhausting conditioned air that the owners had to pay extra to heat.

Another issue would possibly be the flow of air to the kitchen area that previously would have been moving to the return air ducts. How will this air return to the kitchen area?

 

If the restaurant is open to the kitchen, then the EF is drawing air from the entire space, the kitchen is not segregated in any way. Heating is the cost, the owner realizes that cooling performance will be impacted, there is nothing we can practically do about that for such a small installation.
The SA duct and grilles are on the opposite side of the restaurant about 12' AFF, this makes for a good cross airflow. The RA is at the rear of the restaurant about 16' AFF.
If we have the AC in 100% econ for free cooling @ 1600 CFM and the MAU @ say 1400 CFM, what about the excess airflow? The barometric damper is only sized for 1600 CFM.
Dave

 

The true experts in this field are hard at work right now. My business is slow. So, I am able to respond to you during the day. Temperatures are beautiful here in Southern Nevada. So, we have few calls for service work.

If you can hold off until this evening, you will likely get some responses from people who are highly knowledgable.

I have done some restaurant work. Typically the restaurant owners push to have things done as cheaply as possible (understandable). Often they lease the space and don't want to put money into something they don't own. When you "stick to your guns" and refuse to install a system that you know won't work well, you risk losing business to another company. However, if you give in and go the cheap route, they will forever complain about the work you did and possibly ruin your company's good reputation.

 

Seems to make sense to me, I have been in HVAC for 39 years. I'm curious about dumping 3000 CFM into the space. If I exhaust that, then it is also a waste of energy and fan power.

 

Get me as much information as you can on the unit, PARTICULARLY the s#, this way I can bring up the build spec. If you reach me through my private message here I can call you during lunch, open a ticket tomorrow and tell you how to set it up so it will work as efficiently and effectively as possible. Do you know if you've got standard controls operating this system or the M2 or M3??

Sent from my SM-G920V using Tapatalk

 

I have the submittal attached below, I don't have the s/n. I have a very good controls contractor, I used to work for them. If we have to add a stand alone DDC controller, that will not be a problem.

View attachment 673 Topsail Road Restaurant.pdf

 

I told you the true professionals would respond.

 

One problem with using rooftop units for make up air is that the heating works differently. On cold winter days a real make up air unit will modulate its heat to almost precisely maintain a 70 degree supply air temperature all of the time.

A rooftop unit works by turning the heat on and off. That means if it is zero degrees outside you could have full heat blowing out of the vents for a few minutes, then zero degree air for a few minutes, then back to full heat, then zero degree air, and so on. You can see that this probably isn't very good. People generally don't like zero degree air blowing on them in the winter time when they are indoors. Don't think having 2 stages will help much, it really won't.

Never mind the fact that standard rooftop units aren't designed to heat or cool outside air. They're designed to heat and cool room temperature air. Most make up air units that I see can handle a 100 degree temperature rise in heating mode. That means that they can heat the air to 70 degrees down to about a -30 outdoor air temperature. I don't know what the temperature rise of that rooftop unit is, but I would guess somewhere around 40 degrees. That means that if it were to get colder than about 30 degrees outside, you wouldn't be doing anything except for blowing cold air into your space.

You can do what you want, but there is a reason that restaurants have real make up air units instead of trying to jerry rig comfort cooling and heating units like you want to do.


Edit... I see that you're in Canada. The temperature examples I gave were Farenheit. Just wanted to clear that up. I'm guessing heating is important where you are, best not to screw this up.

 

Good advice above. Aside from operational issues there are possibly code issues at play. Many energy codes will not allow an RTU to provide the make up air for kitchens.

 

You'll still need to supply 10-20% fresh air for the dining room. Approximately 20cfm for each person. This will help pressurize the space and keep dining room free of smoke & lower co2 increasing IAQ

Sent from my SM-G920V using Tapatalk