Mini-split for cooling and supplemental heat
mtvhike
4 years ago
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mtvhike
4 years agoRelated Discussions
Do mini split systems come cooling only
Comments (2)Yes, they can be had in cooling-only. I think that the heat pumps are a little more expensive than cooling only, but not much. I can not comment on the relative efficiency. The heat pumps are mechanically more complex so they have more failure modes. I have three multi outdoor units for my seven room house. The reversal valve crapped out on one of mine just before the one-year warranty date. (Note to you AC guys, it stuck in heat mode and would reverse if I tapped on the valve with the butt end of a screwdriver.) I do not think that is a big consideration, but you might want to discuss that. What is the advantage of heat pumps to you? Maybe a lot and maybe none. Do you heat with oil, gas or propane? You can compare your heating costs with your current fuel and electricity rates and decide if you want to heat with heat pumps in relatively mild, but cool, weather. There is a cut-off temp where they fail to perform well when it gets colder. You can zone your heat when you are using them, adding more economy, heating only the rooms are sitting in to comfortable temp and leaving your main t-stat set lower. (This gets a little complicated if the t-stat is in a room that you are heating with the mini split.) Tip: when heating with high wall or ceiling units, you will probably want to turn up the blower manually higher than its programmed speed to keep the heat near the floor and not accumulate near the ceiling. On the other hand, your ceiling paddle fan will take care of this as well if you have them. One thing you might want to keep in mind. I can say that the Mitsu (and perhaps all brand) multi are less efficient than the 1:1 units and they do not do as well as the single units with heating at low temperatures. For the former, I think it stems from the fact that the compressors only throttle back to a certain percentage of max. For example, a single unit might be rated at 9000 BTU. If you only need a little cooling, and assume that they throttle back to 10%, you can efficiently get 900 btu out of them running constantly with no on/off. Your tri unit is probably 22,000 btu and can throttle back to 2200 btu with the same assumption so your compressor will be flicking on and off more often which yields poorer humidity control and not as even cooling. Please, keep in mind the relative nature of my comments. These things all work really well compared to window units and compared to central forced air. Be sure to consider all of your alternatives for the installation. In addition to wall-hung, you can have floor mounted, short ducts to hidden units and ceiling-mounted. That all costs more though. You have probably seen the pictures of installations with the plumbing straight through the walls to the outside of the house. Mine are run inside the walls to underneath the house. Again it might cost you a little more, but talk about it with your contractor. You should look at the MItsubishi, Sanyo, Toshiba and perhaps, other web sites to get some more information about their equipment alternatives. Your contractor should be willing to discuss all of this at length with you since you are making a big investment. I hope they can evaluate your cut off point for economical heating with the heat pumps vs. your hydronic heat. They should be able to estimate for cooling only vs heat pumps. The price difference might be trivial, however....See MoreMini-split options: Mitsubishi Hyper Heat vs. Non-Hyper Heat
Comments (1)Posting again in hopes that someone might be able to comment on Mitsubishi HyperHeat and whether it is worth the additional cost....See MoreElectric Consumption of a Whole House Heat pumps w/mini-splits system
Comments (13)Charles, I found this study https://www.aceee.org/files/proceedings/2004/data/papers/SS04_Panel1_Paper08.pdf which as you implied roughly indicates that a system rated with a HSPF of 11 in Zone 4, at best might achieve aproximately a performance of HSPF = 9 in Zone 5. So adjusting my original calculations, it might be reasonable to expect I will use between 5,500-6,000 kWh per year to produce 50,000,000 btus of heating. Additional kWh will be needed for cooling, but several sources imply that I should only expect to use 1,500 kWh or less for cooling the home. So I think if I make decisions based on needing 7,500 kWh annually to run the system, I will be in the ballpark. One of the nice things about this conversation going back and forth is it made me discover that the cost of natural gas with my utility Eversource has increased from $1.89 to $2.20 per therm, which means I would have nearly $1,100 in future annual natural gas expenditures that altenatively could purchase 4889 kWh of electricity. Adding that to the 3,000 surplus kWh produced by the solar, means I have 7889 kWh available to run the heat pumps/minisplits system. I do understand that this means I am not actually saving any money and in fact get no return on the investment in purchasing and installing the system. The questions comes down to will the system prove to be a better longterm investment compared to replacing our natural gas boiler within the next 3-5 years (expected due to age)? Will the cost of natural gas increase more rapidly than electricity? Will it provide more constant and comfortable cooling and heating (not to mention not having to put in and take out the 4 window ACs as well as the kids bedrooms getting cooling - we don't have window ACs there). Lastly, will the system add value to the resale of the house when we seek to move in 15 years. Your thoughts?...See Moremini split heat pump to supplement central HVAC
Comments (6)10 BTU/sf perhaps? It might be even less. In which case, and this gets to the main question, even the smallest common mini splits at 1 ton / 12,000 BTU could be way over-capacity for any one single room, and therefore end up running in sub-optimal cycling patterns. Inverters or units that have the ability to ramp up and down with 1% increase in loads (heat or cool). The problem is there are many incarnations of Inverters that don't allow a 1% step in capacity. So this is why you really need a trusted pro to do the work for you. The other side of a true 1% inverter step up an down is you pay for over sizing (a bit) because and how the machine runs --- typically starts out slow and ramps up and down as needed you never over supply the space. The over supply the unit has is simply never used, because the algorithm the machine employs doesn't allow it to over supply the space in question. Inverters add more complexity & cost: yes. Everything is moving that way so it's not avoidable for much longer. The con going forward will be how the inverter is designed to operate. 1% step up and down = better. ---- 2, 3, 5 speeds not so good for certain applications (climate is more prone to determine this in my opinion -- mild climates have much less trouble)....See Morearmoured
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