Mini-split + heat pump water heater OR geothermal cool/heat + water heating?
Dear All,
I have read a number of articles on this forum and most seem to favor ductless mini-splits over geothermal. I believe peopel have said performance may be neck and neck while up front costs probably favor the mini-split.
However, what happens when water heating enters the equation? Some background:
I live in Wilmington, NC (climate zone 3). No natural gas is available here. I am purchasing a house that was built in 1998. The intracoastal waterway is 0.7 miles from this home to the east as the crow flies. I believe all systems are original (for sure roof and HVAC are shot). The largest space in the house is a 17×23 (391ft2) living room with angled cathedral ceiling and 2 skylights. It is connected to a 11×28 (approx 310ft2) kitchen/dining area without cathedtral ceilings.
This is our opportunity to retrofit as much as possible (how quickly given budget constraints is another matter)! My plan of attack:
-Get energy audit
-Close envelope + insulate (ceilings,walls, hot water pipes, water heater, etc) + 3M film on windows/doors
-Replace roof – radiant barrier + R30 insulation + light colored metal (no power ventilation since II have read it can be counterproductive)
-Replace HVAC (ductless mini-split? geothermal?)
-Replace water heater (hot water recirculator? point of use electric tankless? air source or geothermal heat pump?)
My question is: given that a air heat pump water heater requires a 10x10x10 room of hot air at all times, how do I manage that when average January temperatures are 56/36 in this area?
Am I relegated to a regular water heater/electric tankless? If so, would a holistic geothermal system make sense because it would provide cooling/heating of the house + hot water?
Also, can a mini-split handle that main living/dining/kitchen area, or would I put 2 in there? And what does one do with the old ducts? Remove, or keep in place?
Would welcome any and all comments, including critique of plan of attack. This will be our forever home, and I want to do things correctly!!!!! (also I am a green newb, just beginning my research journey.
Thanks in advance for your wisdom!
GES74
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Replies
I just read Martin's great article, "Heat-Pump Water Heaters Come of Age" (thank you!) which says that I *can* use a air source heat pump water heater in my zone, but I'm still unclear as to
- how much efficiency I lose by putting it in my utility room (1 story, we have crawl spaces but no basements)
-and therefore, whether geothermal in this instance might be more cost effective?
My suspicion is that most of you will say not - that the incremental cost of a heat pump water heater is much less than the difference in up front costs btw geothermal and mini-splits, but i am still interested in your opinions just in case there are other factors to consider...thanks in advance.
Before you install a heat pump water heater in your utility room, visit soneone who has one. They are pretty noisy. I opted for a regular electric resistance water heater. The HPWH doesn't need to be in a hot room.
I'm in Maine. My great room is larger than your two rooms and a single minisplit is sufficient, but my house is very tight and well insulated. You really need to know your heat load and cooling load to size any HVAC equipment.
I'd do the minisplit and spend the money saved over the ground source heat pump (geothermal) on improving the building envelope and/or a pv system.
I just commented on another thread about a variation on a minisplit that appears to have performance on par with geothermal, and actually better installation flexibility than minisplits. https://www.greenbuildingadvisor.com/community/forum/green-products-and-materials/46941/any-one-have-experience-chilltrix-equipment
There's not much experience/reputation with that company to go on, but it looks great to me. Minisplits could also be good for your situation.
We use heat pump water heaters up here in New England with no problems--down in NC you should have no worries at all. It will be a little less efficient in the winter than the summer, but always substantially better than without the heatpump. If you want to do more for your hot water costs, you could get a drain water heat recovery system for 1/100 the cost of geothermal. http://www.renewability.com/power_pipe/index.html
You can buy them retail from home depot or wholesale from efi.org. By the time the heat pump and the heat recovery each take a big chunk out of your water heating costs, there's not much left to worry about.
In general, you should do your envelope upgrades before the HVAC choice, so that you can buy the smaller HVAC system you then need. So it may be too early to be choosing that before you at least figure out, if not finish implementing the rest of the plan.
So the best focus is on that first step, get an energy audit. If you find a really energy expert to do that, that person can help you with the other decisions as well.
As for what to do with the old ducts, that depends to some extent where they are. Likely tightly sealing them off and leaving them in place is the way to go. But if they are in conditioned spaces, you could consider using them as a way oversized duct system for an ERV ventilation system.
Steve,
Thanks for the idea about visiting someone who has a heat pump water heater, will do. Also, I know that mini-split + PV has been recommended before…great to see it get another vote.
Charlie,
Thanks for the heads up on ChilTrix. I have yet to do a deep dive on it but did do a google search and came up with the following threads, in case they are useful to you:
http://hvac-talk.com/vbb/showthread.php?1792041-Mini-split-geo-system
in addition to ChilTrix, posters mention the following options that you may or may not already know (if you have thoughts, would certainly appreciate it. In particular, I know of a contractor here in Wilmington who handles Waterfurnace products):
- Aqua products - air source
- Multi-aqua - air source
- ClimateMaster - water source
- Waterfurnace - water source
- Samsung - water source
SirReal63 @ http://www.tractorbynet.com/forums/rural-living/336989-mini-split-c-heat-pump-4.html
shared,
"We are probably going with the Chiltrix system. The parent company is HotSpot Energy, and the bulk of their business is in the Caribbean. Their tech support is top notch, they answered all of my questions within an hour and I spoke with John on numerous occasions, he is one of their engineers. If you are lucky enough to get John via email or phone then you will be pleased. No they are not a Fortune listed company but they are a very innovative company. We took a gamble with the 48 VDC mini split, we know that, our Mitsubishi unit has been bulletproof but we were looking for something that was native 48VDC for off grid use, they were the only company I found that offered it. The Chiltrix is brand new, I am not sure if there are very many of them even in use yet, but we plan on giving it a try. My Dad was a refrigeration tech, was a certified chilled systems installer and tech. If he were still alive he would be very excited about this product. If the main house were ready for it today, I would have already ordered a 4 ton system from them and I am a hard sell on just about everything I buy.”
Thanks also for the suggestion re the drain water heat recovery system! Will look into it closely.
Sorry Charlie, started reading in more depth and now realize that ClimateMaster and WaterFurnace are regular geothermal systems. Not sure what the Samsung product is - says something about "DVM S has achieved top class energy efficiency by adopting a dual inverter compressor with vapor injection system. Simultaneous heating/cooling efficiency: as high as 27 IEER, 30 SCHE." I don't have a clue what any of that means.
And maybe multiAqua is similar to the ChillTrix? (looks like it works with ductless mini-splits). Aqua doesn't seem to show any minisplit option.
http://samsungdvm-s.com/downloads/DVM%20S%20Catalog.pdf
Yes, multi-aqua is similar to the ChillTrix, but I think ChillTrix is more efficient, although that's not based on looking the two side-by-side.
The samsung DVM-S looks like larger-than-mini split units with the same or better technology as used in minisplits. The smallest is probably too big for you.
One of the things that I like about the hydronic systems like Chilltrix is that we always hear people worrying about whether their minisplits will heat all the remote rooms adequately--rooms that are too small to merit their own minisplit heads. That might be an overblown fear, as it mostly comes up as a worry in design, not as a problem in actual practice that then needs a solution. But with a hydronic system, it's easy and cheap to add a panel radiator to the room you are worried about to ensure there's enough heat there.
Oh, it's the Samsung "EHS Monobloc" that is a similar product. Water to air heat pumps sized for a moderate size pretty good house. Not sure it's available in the US. Here's the UK page:
http://www.samsungehs.co.uk/
As much fun as it is to evaluate all the different options there, and try to figure out what might be the most efficient, it misses the point of why mini splits are the GBA HVAC system of choice: cheap commodity hardware, without overhead costs (both installation and operating) and design pitfalls of complex distribution systems. That many models have extremely good efficiency in mild weather and decent efficiency in extreme weather is just icing on the cake.
Tim C's Mini Split Retrofit decision tree (when you don't have natural gas):
1. Can your heating & cooling needs be met with no more than two mini split heads? (even if those heads are ducted or need transfer fans for a few rooms)
YES) - mini splits are your most economical option. It would take an enormous efficiency advantage over mini splits to make up for the extra cost of more specialized system (modeling my own home in southern Wisconsin, climate zone 6, I would need an COP of 6 for a GSHP to break even with 2 mini splits over 10 years)
NO) - continue to question 2
2. Does a significant portion of your space conditioning load occur during harsh outdoor conditions where mini split efficiency is low enough to allow some possibility of significant savings? (100F)
YES) - It's possible that alternative systems could be cost effective. If you get good quotes, with quality designs that don't defeat they hypothetical efficiency benefits.
NO) - Either go with mini-splits, or continue to use traditional equipment with your current distribution system.
Without the post-improvements heating/cooling load numbers it's impossible to know optimal solution. . It's downright silly to be throwing out random solutions that may or may not have the right capacities for the loads. Depending on what your automotive needs are you might need a Prius, or you might need an F-150. You wouldn't want the Prius if you need to haul 50 sheets of plywood at a time on a regular basis, and you wouldn't want the F-150 as a commuter car running 100 miles/day.
Those 4 & 5 ton chillers are only relevant for discussion if you have the commensurate loads for it. The ~700 square feet of space described so far would probably have a cooling load of a ton or less, and a heating load that might be covered by a 1-ton mini-split compressor, but that all needs to be calculated.
Wilmington NC's 99% and 1% design temps are +27F and 91F respectively, which means best in class air source heat pumps can meet or beat middle-of-the road geothermal solutions on efficiency, if sized appropriately.
https://www.extension.org/sites/default/files/7.%20Outdoor_Design_Conditions_508.pdf
Given the modest sizes of the spaces, tightened up it's clear that mini-split solutions could work efficiently if sized correctly- even ducted mini-splits, as long as the ducts can remain completely inside the thermal & pressure boundary of the house. With a 1-story house with a sealed-conditioned crawl space, there may very well be a reasonable mini-ducted mini-split solution, but there are probably other options that would be cheaper or more efficient or more suitable depending on the particulars.
Are the two large areas connected with a big archway, or are they remote from one another?
How much west facing window area is there soaking up late-day solar gain, adding to the cooling load?
Is there an attached garage that might be a reasonable location for a heat pump water heater?
Are there reasonable roof pitches & orientation suitable for PV? (A quick & dirty way to figure that out is punching in the address on this site, and clicking on the roof pitches in question: http://geostellar.com/ )
Gina,
You've gotten good advice here.
Ground-source heat pumps rarely make economic sense for residential applications, because the installation and equipment costs are so high. More information here: Are Affordable Ground-Source Heat Pumps On the Horizon?
There is no reason that you can't put a heat-pump water heater in your mechanical room -- as long as your mechanical room is big enough. Before going this route, check the minimum volume requirements established by the heat-pump water heater manufacturer to be sure that your mechanical room is big enough.
Charlie - "Samsung DVM-S looks like larger-than-mini split units with the same or better technology as used in minisplits. The smallest is probably too big for you."
Just got off the phone with Samsung, and they said that their DVM-S Eco starts out at 3 tons and can incorporate up to 6 inside wall units (though brochure says 9). See page 11 of http://samsungdvm-s.com/downloads/DVM%20S%20Catalog.pdf. The gentleman said something about single phase being appropriate for residential.
"with a hydronic system, it's easy and cheap to add a panel radiator to the room”
Thanks for the heads up, that’s great to have in my back pocket1
"Samsung "EHS Monobloc”
Samsung said not in the US yet.
Tim - “mini splits = cheap commodity hardware, without overhead costs (both installation and operating) and design pitfalls”
Thanks for the Cliff’s Notes on benefits (seriously! it gave me clarity) and decision tree. My guess is “no” -> “no” but will keep the tree in mind once the HVAC guys come out to do their assessment.
Dana - “without post-improvement load numbers it's impossible to know optimal solution”
Totally understand. But I’d like to get up to speed on the various options available so that when the time comes I’m already educated and quick to pull the trigger, instead of dragging things out for months afterward. So I really do appreciate everyone’s time and input.
Thanks for the heads up on tonnage, and Wilmington NC outside temp data.
To answer your great questions,
LR opens up to dining/kitchen via no archway - gap is probably 12ft (length) x 10ft (ceiling height)
Garage, utility room, master and master bath face west - master has 2 standard 36” windows, utility room as 1 standard 24” window.
Yes, garage is 2 car attached, current water heater is in there now.
The PV website you mentioned states: 8 solar panels w/ total power capacity of 2.16 kW, or 1,462 kWh/kW of AC energy potential. House currently uses 1,507.91 KWh/m or $159/m so savings would be 17% of electric usage.
(thanks for that last resource, very cool! <- no pun intended, ha ha)
Thanks to all!
BTW: When I peeked at the specs it looks like the smaller Chilltrix chiller is only 2.5 tons, and modulating, and more likely be match output to loads for more homes than a 5 ton 1-speed. In a zone 3 climate you'll still be needing to use glycol in the system to avoid freeze-up. Read the capacity & temperature carefully, there's still plenty of ways to screw it up.
Also note, the COP efficiencies specified are for the chiller only, and doesn't include pumping or control power use. As with GSHP the actual as-used efficiency is highly dependent upon the talents of the system designer- it's not a "system in a can" the way mini-splits are.
http://www.chiltrix.com/chiller-technology.html