MUA Retrofit Case Study

RETROFIT MOTIVATIONS

Project Overview

Located in Greater Toronto Area, Ontario, this property is a 9-storey multi-residential building with an underground parking level, constructed in 1973. The structure is in overall fair condition, though most windows are single-pane with aged weather stripping and limited thermal performance.

The heating plant in the penthouse houses three boilers with a combined input of 5,260 MBH, providing hydronic heating to all suites. The Domestic Hot Water system consists of two RBI boilers rated at 2,020 MBH. Two gas-fired MUA units on the roof supply ventilation air but operate in fan-only mode and show visible deterioration.

The building lacks a central BAS; all equipment is manually controlled through local switches and thermostats. Lighting fixtures are primarily T8 and CFL types. Natural gas remains the dominant energy source, primarily used for space heating and DHW production, while electricity supports fans, pumps, and common-area lighting.

EXISTING MECHANICAL EQUIPMENT

(Pre MUAs system Retrofit)

3 Space Heating Boilers

2 DHW Boilers

2 gas-fired Make-Up-Air Units (MUAs)

No central BAS or zoning control

Lighting: T8 and CFL fixtures

Building sub-metered for suites

UTILITIES	USAGE (Yr)
Electricity (%)	29%
Electricity (kWh)	1,219,075 kWh
Gas (%)	71%
Gas (m³)	276,556 m³

MUAs system Retrofits

As part of an ongoing commitment to energy efficiency and operational improvement, Mann Engineering was engaged to assess opportunities for reducing mechanical system operating costs and optimizing building automation performance at a multi-residential property in Greater Toronto Area.

The project was carried out through a structured three-phase process, beginning with a detailed site visit, followed by data analysis and simulation, and concluding with system performance evaluation and retrofit recommendations.

During the on-site assessment, Mann Engineering reviewed the condition of all major HVAC components, including boilers, make-up air units, and domestic hot water systems, as well as lighting and control equipment. Utility data covering a 12-month period were analyzed to determine baseline consumption and benchmark the facility against comparable buildings across Ontario. The audit revealed that while the overall structure remains functional, much of the existing equipment is nearing the end of its service life. Single-pane windows, aging weather-stripping, and the absence of a centralized BAS contribute to energy losses and higher maintenance requirements. These findings underscored the need for targeted system upgrades to improve comfort, reliability, and energy performance.

SOLUTION Based on the findings, Mann Engineering proposed a Hydronic Make-Up Air Unit (MUA) Retrofit with Variable Frequency Drives (VFDs).

This solution replaces the aging gas-fired MAUs—original to the building—with new hydronic units connected to the existing boiler loop. The integration of VFDs enables airflow modulation according to real-time demand, reducing both energy consumption and operational noise.

The proposed retrofit is expected to lower natural gas consumption by approximately 14,000 m³ per year, translating into annual savings of $7,100 and a simple payback period of 0.7 years. Beyond financial returns, the project improves ventilation efficiency, extends equipment lifespan, and enhances indoor comfort through more stable temperature control.

SYSTEM DESIGN The existing Make-Up Air (MUA) units were aging direct-fired gas systems that provided ventilation and heating but had reached the end of their service life, showing reduced efficiency and increasing maintenance demand. The client initially planned a simple re-re project of the same model of direct-fired gas MUAs at an estimated base cost of $110,000.

However, a direct replacement would not allow for the addition of Variable Frequency Drives (VFDs) due to combustion safety limitations inherent to direct-fired systems, and the resulting return on investment would exceed 20 years, offering minimal efficiency improvement.

To overcome this, Mann Engineering’s engineers proposed an upgraded solution: converting the system to a hydronic MUA with glycol heating coils connected to the existing central boiler plant. This approach not only enables the integration of VFDs for fan speed modulation but also eliminates the need for on-unit gas combustion, improving both energy efficiency and operational safety.

With VFDs, the fan speed automatically adjusts according to demand, avoiding constant 100% full-speed operation. This allows the system to significantly reduce electrical consumption during partial-load conditions, further improving overall energy conversion efficiency.

PROJECT IMPLEMENTATION & INSTALLATION CONSIDERATIONS 

Despite the relatively compact scale of the mechanical room, the retrofit work required careful coordination between design and installation teams. The project involved the replacement of two aging gas-fired Make-Up Air (MUA) units with a new hydronic system connected to the central boiler plant. To minimize construction complexity, the new glycol feed and expansion tank were installed within the existing footprint, while new circulation pumps and Variable Frequency Drives (VFDs) were added to modulate fan airflow and enhance control precision.

A significant project constraint was the tight schedule associated with the incentive program.

All installations had to be completed and commissioned before October 31st to qualify for the full incentive value projects completed after this date would receive only 50% of the available incentive funding given that incentives are one of the key factors influencing payback performance, close coordination among contractors, suppliers, and commissioning agents was essential to meet this deadline.

The retrofit was completed with minimal disruption to building operations, and post-installation testing confirmed stable performance and improved air distribution. With the integration of hydronic heating and VFD control, the new system delivers higher efficiency, lower operating costs, and extended equipment lifespan.

ECONOMIC ANALYSIS Combined, the total project cost for the hydronic MUA retrofit was $150,000, including the new glycol piping, expansion tank, VFDs, and control integration. After accounting for base replacement costs of $110,000, the incremental investment was only $40,000. Through the Enbridge Gas and Save on Energy incentive programs, the project qualified for $35,210 in total incentives.

Estimated annual utility savings include 14,084 m³ of natural gas and 5,793 kWh of electricity, translating into $7,149 in annual cost savings.

The resulting simple payback is only 0.7 years, making this measure exceptionally cost-effective compared to the alternative heat pump MUA option, which required over 90 years to recover investment.

In addition to the direct financial benefits, the retrofit will reduce greenhouse gas (GHG) emissions, enhance air quality, and lower maintenance costs associated with gas-fired components.

				COSTS	ESTIMATED POST-RETROFIT ANNUAL SAVINGS
Annual Cost Savings	$7,149 per year	Category	Energy Saved	Equivalent (ekWh)	Cost Saving ($)
Base Replacement Cost	$110,000	Electricity	5,793 kWh	5,793 ekWh	$811
Incremental Cost of Measure	$40,000	Natural Gas	14,084 m³	145,407 ekWh	$6,338
Estimated Incentives	$35,210	Total	—	151,200 ekWh	$7,149
Simple Payback	0.7 years
Total Installation Costs	$150,000

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