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Community and Q&A

Mechanicals for a well insulated house

GBA Editor | Posted in Energy Efficiency and Durability on

I am looking for the most cost effective heating,ventilation,hot water strategies for a medium sized house with r-30 walls, r -60 cielings in western Ma.

Which ends up being more economical, on demand gas hot water or solar with gas backup?

How cost effective is heat recovery?

I have heard of a unit that combines boiler, hot air,ventilation,hot water in one unit, has anyone used one?

Are there books or articles I should read?

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  1. GBA Editor
    Martin Holladay | | #1

    1. When it comes to the purchase price of the system, it is more economical to use an on-demand gas water heater WITHOUT a solar thermal system. A solar hot water system costs between $6,000 and $10,000 and will have a simple payback period of 40 to 60 years in Mass., before you break even and begin saving money.

    2. Heat-recovery ventilators are NOT cost-effective. In other words, the heat that is recovered is not enough to justify their high purchase price. However, they are the most effective available ventilation systems, and have the lowest operating cost.

    3. The combination unit you have heard about is the Matrix combo appliance from NY Thermal Inc. ( of Sussex, New Brunswick. I haven't installed one.

  2. GBA Editor
    Martin Holladay | | #2

    More on the Matrix:

    Product Review from Environmental Building News
    February 1, 2009
    Matrix Total Home System Offers All-in-One Efficiency

    When NTI founder Kevin Dennison visited western Canada in 1999, he found slab-on-grade houses with air conditioning and heat-recovery ventilation for the summer as well as radiant floor heating for the winter. Looking at all of the separate equipment and the space it required, Dennison wondered, “Why couldn’t we develop a unit that did everything in one cabinet?”

    Designed for houses up to 3,500 ft2 (330 m2), NTI’s Matrix Total Home System does just that, incorporating a high-efficiency, gas-fired condensing boiler and furnace, condensing on-demand water heater, and heat-recovery ventilator into a single unit. Features include efficient, variable-speed, electronically commutated motors (ECM); a microprocessor that adjusts heat output based on actual loads and multiple zones; and a sealed-combustion burner that draws in outdoor air and directly vents exhaust. Because it comes with a 2" (50 mm) rather than 1" (25 mm) pleated filter, the system accommodates better air filtration than most residential-scale equipment. The system is designed for easy serviceability and access, and the boiler operates at a quiet 40 decibels. “You can’t hear them” except when they’re running in some cooling settings, said Derrick Trudgen of Trudgen Heating & Cooling.

    Like all on-demand water heaters, the Matrix saves energy by eliminating heat loss from stored water. But it also uses a more efficient heat exchanger than other tankless water heaters, and the condensing boiler used to heat the water has a combustion efficiency of 98%, much higher than the typical 84% efficiency of other tankless systems. As is typical with on-demand systems, there is a delay of 15–30 seconds before hot water arrives at the tap and a flow rate limitation of 4–5 gallons (15–18 l) of hot water per minute. “They expect this in Europe,” explained Brennan Ferguson at NTI, but “it takes a while to get people on this continent to adjust.“ To address this concern, Trudgen frequently installs the system with a 20-gallon (75 l) holding tank on a recirculation system to prevent a hot water delay—an approach that somewhat compromises efficiency.

    Because the Matrix is a cohesive unit rather than a collection of separate units, evaluating its efficiency is complex. The Matrix earned a Premium designation under a new Canadian standard for integrated mechanical systems. However, it is the only unit to pass the many tests the standard requires, so there are no direct comparators.

    To help consumers evaluate the Matrix against stand-alone appliances, NTI used simulations from Canada’s HOT 2000 energy program, which estimates the efficiency of individual components of the system. These standard efficiency ratings—94% and 92.7% AFUE for forced hot air and hydronic heat respectively, and 0.85 EF for water heating—are quite respectable. But those numbers don’t tell the whole story, says Dennison, who notes that the Matrix’s integration and controls provide 10%–15% energy savings over high-efficiency units operating separately. “Because of the way it is controlled, you can make energy decisions based on total demand and are not redundantly turning on burners for separate appliances,” he told EBN.

    The Matrix is most commonly installed in high-end homes that use forced air as well as some form of hydronic heating, which can range from radiant floors to pool heaters. The system has also been installed in retrofit applications where the integrated water heater and heat-recovery ventilator are attractive. In homes using only forced-air heating, the system isn’t cost-effective. While the Matrix is marketed for homes, NTI uses multiple units in a series to heat and cool its factory, and others are considering the unit for light commercial applications.

    The Matrix unit sells for roughly $7,000 to $9,000. However, for appropriate applications, the Matrix’s installed cost is usually comparable to that of separate units because it costs less to install. According to Trudgen, there can be as much as a $3,000 reduction in installation cost relative to tying together four separate units. “Every home the Matrix suits, we’ve sold one. I’ve never lost a job, because of the savings right off the hop and the small footprint.” [– Jennifer Atlee]

    For more information:
    Sussex, New Brunswick

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