Nelson Mechanical relies on innovative system for Martha's Vineyard residence

Enter Ted Bayne and Lea Delacour. They live on Martha’s Vineyard year-round and heating efficiency is top of mind for these residents. The 3,000-sq.ft. home, which was heated by radiant floors and a Viessmann propane boiler, needed a heating efficiency boost. Their heating goals were threefold: 1) to find a heating source that would make their existing 90% efficient heating system more economical to run; 2) find a system that would not involve destroying their extensive gardens with a geothermal installation; and 3) find a system that would use electricity to operate — making their home ready for the “all-electric” island that Martha's Vineyard will become in the near future.

Annual savings of 54%

Last year, the couple contacted Nelson Mechanical Design Inc. (NMD) to design, engineer and install an innovative heating system that would meet their three goals. The existing system was approximately six years old and represented what once was the state of the art in hydronic heating. Overall system efficiency was on the order of 80% to 90%. There was no realistic or cost-effective way to significantly reduce system-operating costs or improve upon the former levels of energy efficiency, or so the couple thought.

NMD recommended the Daikin Altherma as the solution that uses electricity, operates at geothermal efficiency levels of 200% to 400%, has a tiny outside footprint and heats water for the home's radiant floors and domestic hot water system. At the Bayne residence in West Tisbury, Nelson Mechanical Design installed a Daikin Altherma heat pump system, which is used for radiant heating and making domestic hot water in tandem with an existing propane boiler. The goal of this installation was to demonstrate that a heat pump could work effectively year-round on the Vineyard to comfortably heat a home and make domestic hot water while reducing annual operating costs by more than 40%. The Daikin Altherma provides geothermal levels of efficiency at a much reduced installation cost and can operate all winter long.

In this particular Vineyard home, the Daikin Altherma system works in conjunction with a propane boiler, seamlessly integrating its production of hot water with the existing system while reducing annual operating costs by $3,400. The homeowner's annual electricity bill did go up approximately $1,000, but their annual propane bill dropped from around $6,500 to $2,000, a 54% reduction in annual expense. The innovative coupling of the Daikin Altherma with the boiler lets the Altherma heat pump do most of the heating all winter long and turns on the boiler only on the coldest days.

“Getting Daikin to support running the Altherma continuously throughout the winter was a huge part of this project's success,” said Brian Nelson, principal, Nelson Mechanical Design Inc. “I coined the term co-valent to mean two heating sources running in parallel. Actually, the Daikin Altherma folks confirmed that this approach has been added to their training materials.”

Proof is in the project

Now, after its first year of operation, these projections have been confirmed. The propane and electricity bills for the year indeed showed an annual operating cost reduction of $3,400 or 54% compared to the original propane system. 

“We are all very pleased with the real world numbers that Ted Bayne is now seeing, showing that indeed the heat pump technology is mature enough for widespread island use with savings exceeding even our optimistic projections,” said Nelson.  The heat pump uses electricity to capture stored solar energy in the outside air to make hot water and radiant heating even when the outside air is below 10°F, the heat pump can generate water at 125°F.

The Daikin Altherma project involves integrating an indoor unit with an existing domestic hot water, high temperature radiant panel and low temperature radiant floor heating system. The existing system is built around a Viessmann Vitola 200 propane fired boiler, a Vitotronic 200 control system, a Divicon mixing station and a Vitocell 300 domestic hot water tank. The Divicon serves six radiant zones; each zone has a thermostat that controls its respective circulator through a Taco circulator control. There is one zone of high temperature radiant wall panels served by a high temperature circulator. Both high temperature and mixed temperature boiler circuits utilize heating curves reset using outside temperature. The Vitocell 300 tank is served by a domestic hot water circulator.

Below an initial setting of 40°F, the domestic hot water (DHW) stat will enable boiler burner operation and switch the motorized valves so that the Daikin DHW tank serves as preheat to the Viessmann tank. The Vitotronic control will sense tank temperature and operate the burner and DHW circulator to maintain 130°F in the Viessmann tank. The Altherma output will be devoted to space heating and domestic hot water production will be disabled via a field setting. Above 40°F, the DHW stat will switch DHW roles by changing the motorized valve positions and disabling the Viessmann boiler burner. The Viessmann DHW tank will now serve as preheat and the Daikin DHW tank will maintain 125°F.

“A control (DHW stat) will let us choose the temperature of the changeover between using the boiler or the heat pump for domestic hot water,” said Nelson. “Being able to shut off the Altherma DHW production below this temperature means that we can use all Altherma output for space heating to meet the building heat loss. We determined that over the winter, the heat loss was more hours than the DHW load so it made sense to devote as many Altherma hours to the heat loss to maximize annual savings.”

Bayne and Delacour have not noticed any change in their winter comfort, but their operating costs have been significantly reduced.

“When the Viessmann system and radiant heating became popular about 10 years ago, they were perceived to be the ultimate in heating comfort and efficiency,” said Nelson. “Ten years ago, 90% efficiency looked pretty good. But 90% efficiency is no longer good enough with today's energy prices. The Daikin Altherma brings the efficiency of this system up toward 400%.”

An innovative installation

The installation is innovative in several ways. The existing Viessmann boiler had been set up to heat the radiant floors and domestic hot water. NMD determined that the most effective way to use the Altherma to meet these needs was to split the Daikin's radiant and domestic hot water output.

Above a selectable outside temperature, the Daikin Altherma will do all of the domestic hot water heating and the Viessmann boiler will be off. Below this temperature, the Viessmann will do all of the domestic hot water heating and the Altherma will be off. The two hot water tanks are connected together with automatic valves — when the Daikin is making domestic hot water, the Viessmann tank is serving as a pre-heat tank — likewise, when the Viessmann tank is on, the Daikin tank is the pre-heat tank. This means that all energy used to heat domestic hot water is never wasted, there is always plenty of hot water, and most of the time, the domestic hot water is made at heating efficiencies of 200% to 400% with the Altherma.

Similarly, a selectable outside temperature also controls the radiant heating system. Above this temperature, the Daikin Altherma does all of the radiant heating at heating efficiencies of 200% to 400%. Below this temperature, the Daikin Altherma continues to provide hot water to the radiant floors, but the Viessmann boiler is allowed to add only what additional heat is necessary to maintain inside comfort. This allows the Daikin Altherma to work all winter long, providing heat to the radiant system while significantly reducing radiant heating costs.

A Daikin Altherma outside condenser was connected through refrigerant lines to an inside Altherma hydrobox unit (that extracts the heat from the circulating refrigerant for use in the hot water system). A Daikin motorized valve was installed to send hot water either to a Daikin domestic hot water tank or to the radiant heating system. A control system was installed to integrate the new Daikin Altherma heat pump with the existing Viessmann boiler.

“It took some thought, but we cracked the ‘Viessmann code’ and found a great way for the Altherma to greatly reduce annual operating costs and bring this heating system into the 21^stcentury — quietly, simply and all winter long,” said Nelson.

Click here to view a drawing of the building heat loss vs. heating output: Daikin Altherma and Viessmann boiler.