Fujitsu

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Ductless Minisplits May Not Be As Efficient As We Thought

New England researchers find that minisplits have lower air flow rates and lower COPs than expected

Posted on Oct 16 2015 by Martin Holladay
prime

A recent monitoring study of ductless minisplits installed in seven New England homes found that these heating appliances had lower airflow rates and lower coefficients of performance (COPs) than expected. The average COP of these air-source heat pumps ranged from 1.1 at the house with the least-efficient minisplit to 2.3 at the house with the most-efficient minisplit.

The results of the study raise at least as many questions as they answer. Perhaps the most useful outcome of the study is that it sets up a framework for recommendations that could enhance minisplit efficiency.


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Image Credits:

  1. Photo of dog on floor: Peter Talmage; all other images: Consortium of Advanced Residential Buildings

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How To Buy a Ductless Minisplit

This cheat sheet is intended for designers and builders who are confused by available equipment options

Posted on Jun 19 2015 by Martin Holladay
prime

Green builders usually specify high-performance windows and above-code levels of insulation, while striving to reduce air leaks in their homes. As a result of these efforts, most green homes have relatively low heating and cooling loads.


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Image Credits:

  1. Alex Wilson

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Report on Our Ductless Minisplit Heat Pump

Testing the limits of the air-source heat pump in our new house with this cold weather

Posted on Jan 30 2014 by Alex Wilson

It’s been pretty chilly outside, if you haven’t noticed. A number of people have asked me how our air-source heat pumpHeat pump that relies on outside air as the heat source and heat sink; not as effective in cold climates as ground-source heat pumps. is making out in the cold weather. I wrote about the system last fall, well before we had moved in. Is it keeping us warm? We’ve only been living in the house for a few weeks, but here’s a quick report.


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Image Credits:

  1. Alex Wilson
  2. eMonitor data from Alex Wilson

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Practical Design Advice for Zero-Net-Energy Homes

Marc Rosenbaum answers questions submitted by GBA readers

Posted on Jan 17 2014 by Marc Rosenbaum

First of all, thank you very much to all of you who contributed to this thread. I agree with all of you completely.☺ Remember, the reason Internet discussions are so acrimonious is because the stakes are so low…


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Image Credits:

  1. Chris Laumer-Giddens - LG Squared, Inc.

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One Minisplit or Two?

An architect wonders whether he will need one or two minisplit units to heat and cool his two-story home

Posted on Nov 18 2013 by Scott Gibson

Christopher Vernott is an architect at work on his own home — a tight, well-insulated house in southeastern Connecticut — and the time has come to rough-in the heating and cooling system.

Because of the double-stud wallConstruction system in which two layers of studs are used to provide a thicker-than-normal wall system so that a lot of insulation can be installed; the two walls are often separated by several inches to reduce thermal bridging through the studs and to provide additional space for insulation. construction, triple-glazed windows, and careful air-sealing, his heating and cooling loads are low, he writes in a Q&A post at Green Building Advisor.


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Putting the Duct Back in Ductless

A would-be HVAC designer wonders if a ductless minisplit head can be hidden in a closet and connected to conventional ductwork

Posted on Jul 15 2013 by Scott Gibson

Ductless minisplits have a lot going for them. These high-performance air-source heat pumps operate efficiently at much lower outdoor temperatures than standard heat pumps, and they don't suffer the same energy losses due to leaky ducts. A tight, well-insulated house may need only one or two wall-mounted heads to maintain comfort indoor conditions, in summer and winter.

It's the "wall-mounted" part, however, that not everyone warms up to.


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Image Credits:

  1. Fujitsu
  2. Bob Alsop
  3. Steve Baczek

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Ductless Minisplit Performance During Cold Weather

Does it make sense to turn up the thermostat setting when the weather turns cold?

Posted on Feb 22 2013 by Marc Rosenbaum

I tried an experiment this week during our cold snap. We've kept the door closed to the first floor ell (bedroom and bath) and let it run cold, because the Fujitsu wasn't sized to heat that space too. I opened the door early in the cold snap, and let the heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump. go, leaving it set on 70°F. What I found was that overnight the main space went to 66°F, and the upstairs and back bedroom were 3° to 4°F lower.

My calculated heat loss in these conditions is about 24,000 BTUBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. /hour, and the heat pump is rated at about 17,000 BTU/hour at about 10°F. You'd think it would not be able to keep up.


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Image Credits:

  1. Fujitsu

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Two Years With a Minisplit Heat Pump

We’ve been heating our Massachusetts home for $250 a year

Posted on Jan 15 2013 by Marc Rosenbaum

With the exception of one week in February 2011 where I switched back to the oil boiler to take some data before it went away, the Fujitsu 12RLS has now been heating the house for two years. The dedicated meter for the heat-pump system reads 2,584 kWh. So, it cost about $250 per year to heat our house, in mostly milder-than-normal weather. This is about 1/4 the cost of operating the oil heating system.


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Image Credits:

  1. Fujitsu

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Living With Point-Source Heat

With a single ductless minisplit unit in our living room, our second-floor bedrooms run 2° to 4° cooler than the first floor

Posted on Nov 7 2012 by Marc Rosenbaum

When we yanked the oil boiler, we replaced it with a wall-mounted minisplit heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump. in the main level open area that includes kitchen, dining, living and our little office area. We closed off the first-floor bedroom and bathroom so those rooms are only heated by conductionMovement of heat through a material as kinetic energy is transferred from molecule to molecule; the handle of an iron skillet on the stove gets hot due to heat conduction. R-value is a measure of resistance to conductive heat flow. and air leakage through the walls, and so they get cold — in the high 40°Fs at the lowest last winter.


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Image Credits:

  1. Marc Rosenbaum

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Installing a Ductless Minisplit System

We decided to get rid of our oil boiler and install an air-source heat pump from Japan

Posted on Oct 31 2012 by Marc Rosenbaum

The Island CohousingDevelopment pattern in which multiple (typically 8 to 30) privately owned houses or housing units are clustered together with some commonly owned spaces, such as a common workshop, greenhouse, etc. Automobiles are typically kept to the perimeter of the community, creating a protected area within where children can play. Usually, residents are closely involved in all aspects of the development, from site selection to financing and design. houses were designed to have heat and domestic hot water (DHW) supplied by an oil-fired boiler. (Time for a pedantic distinction: a furnace heats air and blows it around a house, and a boiler heats water which is pumped around the house).

They chose a pretty good boiler: a German Buderus G115. The two-bedroom houses got two heating zones' worth of fin-tube baseboard heat, one zone per floor level. The three- and four-bedroom houses have a third zone, for the first floor ell.


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Image Credits:

  1. Marc Rosenbaum

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