Jump to content
I Forge Iron

Any HVAC experts here who know about split systems?


Recommended Posts

I've got a two story Victorian home that was built in 1906.  It's got a forced air furnace in the basement that only has ducts to two out of four rooms on the second floor.  I'm interested in knowing more about split systems because it seems like I could add a "head" unit in the attic which would provide heating and cooling to all of the 2nd floor rooms, and I could replace the natural gas fired, forced-air furnace with another "head" unit to handle the 1st floor.

The house is just under 2,000 sf, the second floor is probably 850sf of that total.  We're in Northern Colorado so I realize that we will probably need heating coils to supplement the few days a year when it drops below 32 degrees outside.  That being said, we currently have to use electric room heaters in the winter, and window air conditioners all summer, to maintain comfortable temperatures.  

A couple of years ago we solicited quotes to replace our aged forced air furnace in the basement, add A/C, and also add a complete forced-air system in our spacious attic.  When the costs for electrical, gas, exhaust, and drain necessary for adding the attic furnace, totaled up, the cost was pretty significant.

I don't know anyone who has a residential split-system in my area.  I see them all the time in commercial applications, but all of those are engineered.  

Thanks in advance.

Link to comment
Share on other sites

I believe that rather than split systems you are looking for refrigerant heat pumps, which in a multi-room system would be a variable refrigerant flow system - VRF (a split system would just be a cooling system with a remote air cooled condenser and indoor evaporator coil integrated with either a furnace or fan coil unit).  VRF is the fairly new popular system for renovations and I'm considering putting one in in my own home.  They are quiet, allow individual zoning by room, and are very efficient.

There are numerous manufacturer's selling these types of systems (Mitsubishi, LG, Fujitsu, as well as the big names like Carrier, Trane and York - all of whom just rebrand other sources) .  As an commercial electrical estimator for a construction firm I would expect you to have contacts for same.  However, if not, one of the better units, particularly for reliable heating in cold climates, Mitsubishi, is represented by Home Depot (probably what they call the "Mr. Slim" line, M series).  As a heat pump, these units will both heat and cool.  You may even be able to get a tax break based on putting in an ultra high efficiency system, though new government policies may have put the kibosh on those incentives.

Don't be scared regarding the engineering of these systems.  The manufacturer's rep can help you quite a lot with that.

Each manufacturer has slightly different piping systems, but the "head end" unit, as you call it, for Mitsubishi is called a branch box.  The outdoor unit is piped directly to the box and the indoor units get refrigerant piping from it.  I believe that these branch boxes need to be powered as well as getting a dedicated condensate drain.

As regards system size, a reasonable rule of thumb for conventional construction would be to size for around 500 SF per ton of cooling, so for your 2,000 SF house you are talking about around a 4 TR system.  Since this is a residential application you can most likely go for a unit that overall provides either heating or cooling rather than one that allows both in different zones simultaneously.

The last thing you need to be concerned about has to do with refrigerant management.  Most locals limit the maximum refrigerant that can be discharged into a room in the event of a system failure based on the room volume.  In a residence with smaller rooms and an overall house conditioning system, you may exceed these limits (ASHRAE 15).  One good work-around is to connect the small room volumes to the overall residence using jump ducts.  Your existing duct heating system may be able to be modified to suit.

Good luck

Link to comment
Share on other sites

I am no expert!  I do have one in my new shop.  It works great and seems very efficient!  QUIET, requires no backup system.  I like the no freeze setting that keeps it about 52 degrees all winter.  I rarely change it till summertime.  We put one in our rental cabin and it eliminates worry over unsafe portable heaters and provides efficient, trouble free cooling as well.  We are very happy with ours!

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...