Question: How to Make Condo MAU More Energy Efficient?

[nielkfj]

First time poster on this forum. Not sure if I should be posting in the residential or commercial section.

My questions are about a make-up air unit (MAU) for a small condo building (12 apartments) where I live, in Canada (i.e. cold climate). The building is a four story wood framed structure built in 1979. The MAU is an Engineered Air model S225/O/R which feeds air to three hallways in the building, pressurizing them slightly.

Myself and some of the other owners are interested in optimizing the energy efficiency of this MAU, and the building in general. So I want to educate myself on what the options are so that I can discuss the issue intelligently with a professional.

My questions:

1) What considerations should be made in determining the hallway temperature set-point for the building?

2) What is the typical range of temperature set-points for hallway air supplied by an MAU.

3) Are there any code requirements for the temperature of condo building hallways?

4) Is it possible to change the air flow rate from an MAU? If so how is this typically done?

5) Are there any code requirement for the air flow rate to hallways from a MAU?

6) Are there any other common ways to make a standard MAU operate more energy efficiently?

Any suggestions would be appreciated.

[nielkfj]

I live in a small condo building. Myself and some of the other owners are interested in improving the energy efficiency of the building. One of the things we are considering is adjusting the temperature and/or air flow rate from a make-up air unit (MAU) that supplies air to the building hallways.

With respect to this, the questions I have are:

1) Other than the comfort level of the temperature in the hallways, are there any other factors that we should be considering?

2) Is there a simple way to adjust the air flow rate from a MAU?

3) Are there any other common ways to make a standard MAU operate more energy efficiently?

Any suggestions would be appreciated.

[ammoniadog]

The make up air unit's purpose is to replace the air that is being sucked out of the building by things like bathroom or kitchen exhaust fans, dryers, and gas burning appliances. I have also heard that maintaining a slightly positive building pressure can help keep out bugs. If a building is in a negative, things such as natural draft water heaters and boilers might not draft correctly and could cause a dangerous carbon monoxide situation.

Ideally a building's pressure should be neutral to slightly positive. In my experience though, most buildings instead seem to be in a slight vacuum.

How is your building? You probably don't want to hear this, but you likely should be thinking of increasing the blower speed, not slowing it down.

[nielkfj]

The make up air unit's purpose is to replace the air that is being sucked out of the building by things like bathroom or kitchen exhaust fans, dryers, and gas burning appliances. I have also heard that maintaining a slightly positive building pressure can help keep out bugs. If a building is in a negative, things such as natural draft water heaters and boilers might not draft correctly and could cause a dangerous carbon monoxide situation.

Ideally a building's pressure should be neutral to slightly positive. In my experience though, most buildings instead seem to be in a slight vacuum.

How is your building? You probably don't want to hear this, but you likely should be thinking of increasing the blower speed, not slowing it down.

I think we have pretty good positive pressure in our building. If I put my hand at the bottom of the entrance door to my apartment, I can feel air blowing lightly underneath the door from the hallway.

In fact I am thinking there is too much positive pressure. The MAU was not working for a week or so in October this year. During this time I noticed that my apartment was about 2 degC (4 degF) cooler during the night. I figure this was because the MAU pushes warmed air continuously into my apartment from the hallway when it is working.

I would like to set it at the minimum acceptable temperature and flow rate, to save some money on heating the air and to have better control of the temperature in my apartment. The temperature is easy to adjust, but the flow rate I don't know if there is a way to do this. And for both temperature and flow rate I'm not sure if there are code requirements as to what the settings must be.

[icy78]

It needs to be looked at by someone who can "see" the whole building picture. Mechanical as well.
Small MUA savings realized by lower MUA cfm and temperature may become big building $ losses in a few years.

Sent from my SM-G950U using Tapatalk

[nielkfj]

It needs to be looked at by someone who can "see" the whole building picture. Mechanical as well.
Small MUA savings realized by lower MUA cfm and temperature may become big building $ losses in a few years.

Sent from my SM-G950U using Tapatalk

Do you know where we should look for an HVAC expert that can look at the entire building?

We have a mechanical maintenance company that maintains the MAU and other equipment. Should we have them do this, or would it be better to bring in somebody from a company that installs MAUs, or a company that manufactures MAUs?

[dan sw fl]

I live in a small condo building.

Myself and some of the other owners are interested in improving the energy efficiency of the building.

One of the things we are considering is adjusting the temperature and/or
air flow rate from a make-up air unit (MAU) that supplies air to the building hallways.

With respect to this, the questions I have are:

1) Other than the comfort level of the temperature in the hallways,
are there any other factors that we should be considering?

HUMIDITY CONTROL

2) Is there a simple way to adjust the air flow rate from a MAU?

__ AUTO ADJUST DAMPER would be standard on MAU.
… Damper would be controlled by providing ~ 0.05" W.C. Positive Pressure

3) Are there any other common ways to make a standard MAU operate more energy efficiently?

CO2 Controller may be an alternative in a few situations.

_ Might wish to think about manually opening window during Clothes Air Dryer use.

Control the TIMING AND AMOUNT of exhaust air from EACH Condo.

ASHRAE STD. 62.2 - 2013
___ Understand & Use the INFILTRATION CREDIT _ _ from data provided by a BLOWER DOOR TEST

For example,
_ 30 CONDOS * ~ 40 CFM / CONDO = 1,200 CFM Total Continuous ( weekends )
__________ 40 CFM Could be less than a Continuous flow rate.
______ … … No one home during the day _ _ Reduce exhaust air flow rate for upto 12 hours

https://www.energy.gov/sites/prod/fi...ily_walker.pdf

[pecmsg]

You need a Mechanical Engineer. There are several factors involved, Building code and Fire Codes. Residential building Common areas are Positive pressure. Hallways, Emergency stairs Etc. Air changes per hour requirements need to be meet!

[buford]

Is the MAU using gas for fuel? And do each units have a gas fireplace? I have seen condos where the gas is on a common meter and during the winter, the fire places are on and drives up usage.

[Juan Madera]

Big capital expense, but might consider an air-to-air heat exchanger that takes all the exhaust air (bath vents) from the building in a common duct and transfers the recovered heat into the supply air. Supply air will be cooler than what you have now, but economy of operation is worth the look.. All the new hotels I've seen use these.

As to efficiency of MAU, if it is a direct fired type, it is 100% efficient. Engineer is recommended in any case, one that has actually worked hands on in the field is preferable..

[Juan Madera]

double..

[icy78]

IMO, you need a good tech, who can also think like a mechanical engineer.
Or a good mechanical engineer, who has a tech who can make the ME's design work properly.

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[ammoniadog]

As to efficiency of MAU, if it is a direct fired type, it is 100% efficient.

Ha, I was waiting for someone to say this! It don't get more efficient than 100%, well unless it's a heat pump, but I've gotten into some heated arguments about how it's impossible for heat pumps to defy the laws of physics, so I'm not going to go there.

With that being said, I believe direct fired units are banned from areas where people sleep, so I'm guessing it has heat exchangers.

I think we have pretty good positive pressure in our building. If I put my hand at the bottom of the entrance door to my apartment, I can feel air blowing lightly underneath the door from the hallway...

This doesn't prove anything other than that your apartment is at more of a negative pressure than the hallway is. A better test would be to go down near the water heaters/boilers when they're not running and hold a match near the flue pipe and see which direction the flame goes (assuming that they're natural draft with no dampers), or go near an outside door to the building and do the same thing with the door slightly cracked.

[nielkfj]

HUMIDITY CONTROL

I'll keep humidity control in mind. But Calgary is fairly dry, if anything we could probably use higher humidity.

__ AUTO ADJUST DAMPER would be standard on MAU.
… Damper would be controlled by providing ~ 0.05" W.C. Positive Pressure

Interesting. I didn't know that. If it has an auto damper that controls the air pressure that would be ideal. I'll ask the manufacturer.

Is there some sort of small compressor built into the MAU that provides the air pressure to control the damper?

CO2 Controller may be an alternative in a few situations.

Not sure what you mean here. The MAU only supplies air to hallways (and the boiler room), not a garage, if that's what you mean.

_ Might wish to think about manually opening window during Clothes Air Dryer use.

I guess that would reduce the amount of air going through the MAU. But I imagine the amount of energy savings would be minimal, and people are unlikely to do this in the winter when the weather is cold.

Control the TIMING AND AMOUNT of exhaust air from EACH Condo.

ASHRAE STD. 62.2 - 2013
___ Understand & Use the INFILTRATION CREDIT _ _ from data provided by a BLOWER DOOR TEST

For example,
_ 30 CONDOS * ~ 40 CFM / CONDO = 1,200 CFM Total Continuous ( weekends )
__________ 40 CFM Could be less than a Continuous flow rate.
______ … … No one home during the day _ _ Reduce exhaust air flow rate for upto 12 hours

A lot of information to absorb here, but at first glance it looks like an interesting possibility - beyond what I had in mind, but perhaps a re-think of the ventilation system for the whole building would be worth it if the energy savings are large.

According to some old drawings that I have, the original MAU (replaced 12 years ago) was rated for 1,500 cfm. The square footage of the entire building, 12 apartments and all common areas, is roughly 18,000 sqft (not all areas are ventilated by the MAU). Assuming the current MAU has the same flow rate, does 1,500 cfm seem excessive?

[nielkfj]

You need a Mechanical Engineer. There are several factors involved, Building code and Fire Codes. Residential building Common areas are Positive pressure. Hallways, Emergency stairs Etc. Air changes per hour requirements need to be meet!

I see. I was kinda thinking it would require an engineer if the air flows are changed.

However, I think the first thing that needs to be done is to find out if the current MAU system is operating as intended. Perhaps it is providing too much flow rate. Do you know how this would be checked? Would this typically be done by a maintenance technician?

[nielkfj]

Is the MAU using gas for fuel? And do each units have a gas fireplace? I have seen condos where the gas is on a common meter and during the winter, the fire places are on and drives up usage.

The MAU is indeed gas fired, but there are no gas fireplaces in the building.

However, the boiler and hot water heater are also gas fired and there is only one meter for the whole building, as far as I know. So we don't actually know how much gas the MAU uses. But I think it will be much more than the boiler and water heater combined, since the MAU runs continuously 24/7 and heats air from sometimes sub-zero temperatures to room temperature. Whereas the boiler is normally only maintaining room temperature in each zone.

[icy78]

I'll keep humidity control in mind. But Calgary is fairly dry, if anything we could probably use higher humidity.



Interesting. I didn't know that. If it has an auto damper that controls the air pressure that would be ideal. I'll ask the manufacturer.

Is there some sort of small compressor built into the MAU that provides the air pressure to control the damper?



Not sure what you mean here. The MAU only supplies air to hallways (and the boiler room), not a garage, if that's what you mean.



I guess that would reduce the amount of air going through the MAU. But I imagine the amount of energy savings would be minimal, and people are unlikely to do this in the winter when the weather is cold.



A lot of information to absorb here, but at first glance it looks like an interesting possibility - beyond what I had in mind, but perhaps a re-think of the ventilation system for the whole building would be worth it if the energy savings are large.

According to some old drawings that I have, the original MAU (replaced 12 years ago) was rated for 1,500 cfm. The square footage of the entire building, 12 apartments and all common areas, is roughly 18,000 sqft (not all areas are ventilated by the MAU). Assuming the current MAU has the same flow rate, does 1,500 cfm seem excessive?

That's a tiny MUA.
Probably everyone was thinking at least 6-12000 cfm.
Also, are you sure it doesnt use some return air?
Altho 1500 ÷ 18 is only about 80cfm per apartment, so it's probably sized to make up the exhaust air.

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[nielkfj]

Big capital expense, but might consider an air-to-air heat exchanger that takes all the exhaust air (bath vents) from the building in a common duct and transfers the recovered heat into the supply air. Supply air will be cooler than what you have now, but economy of operation is worth the look.. All the new hotels I've seen use these.

As to efficiency of MAU, if it is a direct fired type, it is 100% efficient. Engineer is recommended in any case, one that has actually worked hands on in the field is preferable..

Ya, probably a big capital expense and unlikely to be accepted by other owners. What I'm focussing on is trying to optimize the efficiency of the existing equipment. I figure that means reducing the supply temperature from the MAU, and reducing the flow rate if possible. It seems like there is no code restriction on the supply temperature. However, reducing the flow rate is restricted by code. That's where the engineer would be needed I assume.

Another option mentioned is installing a programmable thermostat that will set the hallway temperature back during the night.

I sure hope the MAU isn't direct fired. I'm pretty sure it is indirect, otherwise we would smell natural gas from time to time I would think.

[nielkfj]

That's a tiny MUA.
Probably everyone was thinking at least 6-12000 cfm.
Also, are you sure it doesnt use some return air?
Altho 1500 ÷ 18 is only about 80cfm per apartment, so it's probably sized to make up the exhaust air.

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I'm quite sure there is no return air going into the unit. I've been up on the roof and took photos. Just checked the photos now and there is definitely no ducting going into the unit upstream of the fan.

There's only 12 apartments. So 1,500 ÷ 12 = 125cfm per apartment.

For some reason the hallways for the two basement apartments do not have any make-up air. I might be because both of these apartments have their own hallway with no other apartments sharing that hallway.

[dan sw fl]

I'll keep humidity control in mind. But Calgary is fairly dry, if anything we could probably use higher humidity.

Interesting. I didn't know that. If it has an auto damper that controls the air pressure that would be ideal. I'll ask the manufacturer.

___________
_______ I suspect damper may have electrical controller. ___ ie.. Belimo or similar

Is there some sort of small compressor built into the MAU that provides
the air pressure to control the damper?
___________

Not sure what you mean here.
The MAU only supplies air to hallways (and the boiler room), not a garage, if that's what you mean.

I guess that would reduce the amount of air going through the MAU.
But I imagine the amount of energy savings would be minimal, and
people are unlikely to do this in the winter when the weather is cold.

A lot of information to absorb here, but at first glance it looks like an interesting possibility -
beyond what I had in mind, but perhaps a re-think of the ventilation system
for the whole building would be worth it if the energy savings are large.

According to some old drawings that I have, the original MAU (replaced 12 years ago)
was rated for 1,500 cfm.
__ Actual set-up and rating would not necessarily be the same.

The square footage of the entire building, 12 apartments and all common areas,
is roughly 18,000 SqFt (not all areas are ventilated by the MAU).

Assuming the current MAU has the same flow rate,
does 1,500 cfm seem excessive?

12 CONDOS _ 2 BEDROOMS _ ~ 1,200 SQ FT EACH

ASHRAE 62.2 -2013

Required Make-Up air flow rate would be in the Ball park of 30 CFM
after an Infiltration Credit of 30 CFM is used.

The existing Infiltration amount must be verified by an actual Blower Door Test.

EXAMPLE WORK SCOPE:
_________ One OPTION

Hallways = 0.03 * ~ 3,000 = ~ 90 CFM

12 * 30 CFM = 360 CFM
____________+ 90 CFM
___________+ ___ ___ any Make-up Air for any other COMMON Areas
_____ Total < ~ 600 CFM.

POSITIVE PRESSURE MUST BE MAINTAINED in Hallways.

It appears that 1,500 CFM is excessive IMO.
However, your local requirements may be based on
a Canadian IAQ standard that I am not familiar with.

NOTE: Hallways are not considered to have Occupants.

AHJ in applicable Calgary Building Department / Disciplines
should review your proposed MAU plans.

AUTHORITY HAVING JURISDICTION

ANY STRUCTURAL CHANGES WOULD BE SUBJECT TO LOCAL PERMITING PROCESS IMO.