2021 Webinar Series - 7 Ductless Solutions

Ductless technology has taken the world by storm. Ductless systems offer targeted cooling and heating comfort to zones in residential and commercial buildings. In existing buildings with no central AC, a ductless system may offer the most practical solution to a zoned cooling system – and take over the heating as a significant bonus. While generally thought of as an air-source heat pump technology, many manufacturers have water-source units capable of operating as ground source heat pumps. Our presenters will present examples of product types and example projects.

Ductless Solutions: Using Hydronic Fan Coils, Splits & VRF Tuesday, May 18 | Noon to 1:00 p.m. ET








  1. Is the DHW system separate from the original boiler?
    1. The domestic hot water is produced from a tankless coil in the oil boiler.  They are still using the oil boiler for hot water, but are evaluating their options to retire the oil boiler.
  2. Can you share any cost info for the project?
    1. After incentives through Clean Heat Program - air source heat pumps had incremental cost but the heat pumps really improved the building
  3. Jon - for the Multifamily building case study - did the building undertake any efficiency measure prior to electrifying?
    1. The building was already relatively efficient with newer windows and all LED lighting in common areas.  Following the heat pump install, the building is currently performing some air sealing measures - but nothing extensive
    2. Also answered live.
  4. How was ventilation handled for apartment buildings with the multi-heat pump VRV systems? Are you relying on natural ventilation via the existing windows?
    1. No ventilation improvements were part of the scope.  They are relying on natural ventilation.
  5. For Jon:  Are multi-split air source or water-based hydronic systems feasible and affordable to replace boiler/radiator systems in single-family homes or are they really just for commercial and multi-family buildings?
    1. Air-source multi-split systems are accessible for nearly all single family homes. For other water-based systems, there are a number of variables that would impact the cost of those systems.
  6. Can the water-water systems use existing radiators or would those have to be replaced with hydronic fan coils? And are those affordable for residential applications?
    1. Answered live - It depends. If it’s a cast iron radiator - probably not. If it's a modern baseboard heating system 50% chance it will work. Relatively affordable. 
  7. The second presenter said that boiler backup was needed whenever ground temperature was below 65ºF. Why was that the case? Didn’t they use a compressor to extract heat from the supply water? If not, then why not? Many GeoExchange only systems are installed and work well without boiler backup. Why does their system require boiler backup?
    1. Answered live - the system doesn’t require boiler back up below 65. Since most applications of the water-source VRF are boiler/cooling tower configurations, the boiler might be set to go on at 65F to keep the units in their highest efficiency range.   But you can figure out the de-rate - for lower water temperatures, like when linked to a geothermal closed ground loop.  It is also possible to have hybrid applications with a ground loop assisted by a boiler or a cooling tower, but that’s up to the designer taking into account many factors, like building use, climate zone, cost of energy, project budget, etc. 
  8. Locally there were some air to water projects and the COPs were less than impressive. Do you have COPs for the various systems you’re presenting on?
    1. Answered live. Average is about 2-2.5 COP - energy savings compared to oil system. Tough to measure exactly. Geo systems tend to have a lower operating cost compared to air source systems - but air source systems are still good solutions
  9. Jon - how many winters has the unit you focused on been running?  How has it handled the coldest days of winter without backup?  Do have data on the Coefficient of performance on the coldest days.
    1. The system was commissioned in September of 2020, so we have one full winter of data. We’ve been in touch with the residents, and have confirmed all were comfortable, that the heat pumps were used for all heating, and there was no need for any back-up heating.  One of our measurement partners is planning to obtain cold-weather COP data, however those measurements were delayed due to COVID.  We hope to collect that information during this upcoming winter.
  10. Can Kyle explain more the difference between the system he's describing and a regular geothermal system that doesn't need backup?.  I was shocked to see a backup fossil fuel system needed on any type of heat pump system at 50 degrees.
    1. Answered live. In heating systems - usually 9 degrees difference from the loop - once you hit 41 degrees the system will go into a “freeze prevention mode”- doesn’t shut it down but will speed up the system which impacts it’s performance but keeps it from freezing - glycol (anti-freeze) will prevent freezing at lower temperatures. Really a discussion on what to do when the ground hits 50 degrees.
  11. The Housing Panel of New York’s Climate Action Council has called for ending installation of fossil fuel heating equipment after 2025 or so. The UN’s International Energy Agency (IEA) recently made the same recommendation. Does it make sense to talk about fossil fuel backup when it appears that it may only be legal for a few more years?
    1. Mitsubishi water-source VRF does not “require” fossil fuel back up if a ground loop is designed appropriately - but that’s up to the designer and based on many considerations.  That being said, here are a number of other stakeholders that need to be as comfortable with the heat pump only technology and its capabilities before questions about fossil-fuel auxiliary & backup no longer exist.  If a legacy fossil-fuel heating system is left in place, for risk averse designers the option for building owners to keep that as a source of aux or emergency back-up heating. We are aware that 100% building electrification is the goal and as a manufacturer we have a large range of products to support that direction.
  12. For systems being installed as air source, is any consideration being given to make them easily "geo ready" when a loop or district thermal becomes available?
    1. Air-Source and Water-Source outdoor units are completely different technologies but a lot of the downstream indoor units are compatible and interchangeable.  It’s easier to convert air-source to water-source, change some piping mains, and re-charge the system with the appropriate amount of refrigerant so long as the system “type” is the same (Heat Pump v. Simultaneous).  VRF Heat Pumps do not require a branch box but VRF Simultaneous Heat Recovery Heat Pumps do require one.  
  13. Hi Zach - In the European housing retrofit model known as Energiesprong, gas-fired boiler heating systems are being replaced with air-to-water heat pumps that connect to existing hot water baseboard distribution systems.  This works effectively when the buildings are also retrofitted with well-insulated envelopes.  NYSERDA is trying to mimic this model with the RetrofitNY program. Our winter temperatures are more severe than those in Europe.  What is the prospect of doing this type of retrofit here with either air-source or ground source heat pumps?  Can adequate water temperatures be delivered to keep residents warm and what would those be?
    1. Answered live. With insulation - you will be able to bring down building loads and make them more cost effective