Mariposa: IPS in Large-Scale Housing

Overview

Mariposa is a multi-phase, mixed-income housing development at 1425 Mariposa Street in Denver, Colorado. Denver Housing Authority used this project as a real-world comparison of HVAC technologies, installing different systems across five phases: Mariposa II, III, IV, VI, and VII.

The result was a controlled “shootout” comparing IPS, PTAC, VRF, ground-source heat pumps, and conventional systems—with performance data tracked from 2015 to 2018.

The Five-Phase Comparison

Phase	System Type
Mariposa II	PTAC
Mariposa III	IPS (Williams)
Mariposa IV	VRF
Mariposa VI	IPS (Williams)
Mariposa VII	Ground-Source Heat Pump

Mariposa III is a four-story, 130-unit building that served as one of two IPS test cases.

System Configuration

The IPS installations use domestic water piping for both hot and chilled water delivery to fan coil units. Key specifications:

• Fan coils: Custom-built, averaging 24,000 BTU capacity
• Certification: NSF/ANSI 61 & 372 certified copper coils rated for potable water
• Controls: Individual thermostats in each unit
• Style: Hideaway fan coils with free return and ducted supply
• Economizer: Free cooling available for approximately half the cooling season

Measured Performance (2015-2018)

The three-year comparison produced clear results:

System	Annual Cost per Sq Ft
IPS	$0.69
PTAC	$0.73
GSHP	$0.82
VRF	$0.87

IPS outperformed PTAC by $0.04/sq ft, ground-source heat pumps by $0.13/sq ft, and VRF by $0.18/sq ft annually.

First Cost Comparison

IPS delivered both lower operating costs and lower first costs:

• IPS first cost: $19.04/sq ft (mechanical and plumbing combined)
• Savings vs. alternatives: $2.03 to $6.38 per square foot

Maintenance Impact

Annual maintenance savings with IPS compared to alternatives:

• vs. PTAC: ~$0.06/sq ft annually
• vs. VRF: ~$0.12/sq ft annually

Over a 20-year lifecycle, these differences compound significantly.

Takeaways

• Measure before specifying: Denver Housing Authority’s multi-system comparison provided real performance data rather than relying on manufacturer claims.
• IPS won on all metrics: Lower first cost, lower operating cost, lower maintenance cost.
• Economizer advantage: Free cooling for half the season reduces compressor runtime and energy consumption.
• Scalability confirmed: IPS performed consistently across both Mariposa III and VI installations.

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Source

Williams Comfort Products, Mariposa: Integrated Piping System Outperforms, accessed February 2026, https://williamscomfort.com/projects/mariposa-integrated-piping-system-outperforms/