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Which is more efficient: a geothermal heat pump or a Hyper Heat inverter heat pump?

geobilly | Posted in Energy Efficiency and Durability on

A Mitsubishi Rep. had posted a load run comparing there two systems stating that Hyper Heat Inverter would cost twice the cost of geothermal systems including installation.

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  1. GBA Editor
    Martin Holladay | | #1

    I'm not sure whether you are asking about the cost to purchase and install the equipment, or the efficiency of the equipment, or both.

    A "geothermal heat pump" is more accurately called a ground-source heat pump. A ground-source heat pump will almost always cost more to install than an air-source heat pump or a ductless minisplit system.

    Hyper Heat is a trade name for a type of Mitsubishi air-source heat pump (a ductless minisplit). Such a system will cost less to install than a ground-source heat pump.

    If the system is perfectly designed, perfectly installed, and carefully commissioned -- all very big ifs -- a ground-source heat pump will be slightly more efficient than a ductless minisplit system. But the energy savings (even over one or two decades) may not be enough to justify the higher installation cost of a ground-source heat pump.

    If the system is haphazardly designed, haphazardly installed, and imperfectly commissioned, the ground-source heat pump can easily have a lower efficiency than a ductless minisplit system.

  2. Expert Member
    Dana Dorsett | | #2

    The answer is extremely site and climate dependent, as well as equipment-sizing dependent, and it's a moving target- both mini-splits and ground source heat pumps (GSHP) are seeing incremental improvements in system efficiency over time.

    There are temperate climates (US zone 3-ish) where the annualized average efficiency of a best-in-class mini-split could edge out the heating season efficiency performance of a pretty-good dirt-to-ducted-air system on an annualized average basis, and others (cooler parts of Ontario & Quebec,. most of Manitoba & Saskatchewan) where the heating season efficiency of a mini-split would only be about half or less that that of a ducted-air GSHP system. (Is that where you are located?)

    The highest efficiency GSHP systems use low/very-low temperature hydronic heat distribution (pumped hot water), using concrete slabs as the radiator(s), and highest efficiency ECM-drive pumping on both the ground loops and the radiation end. Done right some of these systems can sometime meet beat 5.0 as the annualized average coefficient of performance, even on an all-in basis (all pumping power accounted for), whereas ducted air struggles to beat 4.0 (which it can, with ECM drive air handlers and simple short ducting). Most real world GSHP systems in a US climate zone 5 & 6 locations average in the low 3s or less if ducted air, 4-ish if hydronic, primarily due to lower-efficiency or sub-optimal pump choices and/or duct designs. A pretty-good mini-split will average a COP of 4 or better in most US climate zone 3 locations when sized properly for the heating loads, but only 3.5-ish in zone 4, or 3-ish in zones 5 & 6.

    With GSHP the efficiency realized is in the hands of the system designer & installer, and every system is a customized build. By contrast mini-splits are canned-systems- it takes some cleverness to really screw up (though there are plenty of clever installers up to the task. :-) ) The cost of just the DESIGN of a best-in-class GSHP system can be higher than the installed cost of a best in class mini-split.

    The installed cost of a GSHP varies a lot by region and site subsoil type. The AVERAGE cost of 3-6 ton systems that qualified for rebates under a recent program in Connecticut (warm edge of US climate zone 5), was about $9 KUSD per ton. A typical 1-ton mini-split installation in CT would be about $3.8K, well under half the installed cost, and an efficiency that is at least getting close to the average real-world all-in efficiencies of GSHP in that region. But a mini-split is point source heating, whereas GSHP is typically installed with radiation or air ducted in every room. In high-performance homes where the heat loads have been designed/adjusted to keep the doored off rooms remote from the mini-split head(s) from having too large a temperature differential mini-splits work just fine, and have become a preferred heating/cooling for many high performance home builders, even in US climate zones 6 & 7, but for a retrofit on a pre-1980 code-min house some amount of auxiliary heating would usually be required to take the mini-split route in colder climate zones. ( I have relatives in US marine 4 who do OK with mini-splits in their less-than-super-insulated houses, with little or no use of supplemental heat beyond the mini-split.)

    There are times when spending the up-front difference in cost on grid-tied photovoltaic solar would more than make up any shortfall on the efficiency end, and this is becoming more true every day. In 2012 the average cost of residential rooftop PV in the US was a bit over $5/watt (prior to any subsidies), 2013 is looking like it'll be falling to the mid $4s, but in locations where the permitting & inspection have been streamlined and multiple competing installers are operating in can be much less. According to Jigar Shah (a founder of Sun Edison, a 3rd-party ownership model solar company) one installer was projecting $1.65/watt for 2014 in some of the hotter markets in Texas. In Germany where it's a somewhat more mature market and quite competitive, the average in recent years has been in the $2-2.50 range, which is where it is POST-SUBSIDY for much of the US (where annual output per watt of rated panel is significantly better too.)

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