Check it out… our Fujitsu 15RLS2 ductless mini-split heat pump got installed this past Friday! Initial thoughts… I like it a whole lot, but there are definitely a few things to keep in mind with this technology. More about this later… first pictures of the install!
This is where I spend all my time during the cold winter days, is adjacent to my bedroom, and connected to the rest of the house through a set of large double sliding doors. By installing the heat pump directly above my mini beverage refrigerator, pointing towards the largest portion of the house, I’m hoping to heat the largest portion of the house/air and maximize savings.
It seemed like a pretty straightforward install, with a single heating contractor spending maybe 2 hours on the inside, and 4 hours on the outside, and the two electricians 2 hours wiring the new 240 V line to the panel, pulling a long feed across the house, and installing a disconnect next to the heat pump.
How’s it Working?
Quite awesomely! But there are still a few things we’re figuring out… particularly the best way to get it integrated in and working with our radiant heating system, and how to get the warm air to some of the, now, colder rooms.
Let me explain…
After installing the heat pump we needed to adjust the thermostats down for two of the radiant zones to take advantage of the cheaper heating price of the heat pump. So, the thermostat for the heat pump is set to 74°F (yeah I know… I get cold easily!), the radiant heat zone for my section of the house set to 70°F, and the radiant zone for the main section of the house set to 68°F. The thinking here is any time the heat pump can make enough heat to heat the majority of the house I’ll let it, and since I get cold so easily, if it ever has a hard time keeping up I’ll kick the slab on to make up the difference. Probably most people would allow for a greater temperature difference between their heat pump and primary heat source thermostats to maximize savings. I’ve also added an additional time in the programmable thermostats for the two radiant zones to kick on the heat of the zones for 30 minutes at 4 AM. This might be totally unnecessary, but I want to make absolutely sure the water in our concrete doesn’t get too cold by running the heat pump (causing those radiant zones to never heat up the concrete).
Any thoughts on this, oh so smart home building/energy efficiency people? Do I need to cycle my radiant to keep it from freezing, or is the insulated slab enough within the building envelope to keep that from happening?
Another challenge I’m trying to figure out related to this, is by using the heat pump, the radiant zone for my section of the house is being used significantly less, which means the warm water is no longer flowing underneath the floor in my bedroom/bathroom. One would hope that the warm air from the heat pump would be making it into these areas, but due to how it blows/directs the heat straight ahead my bedroom and bathroom are now cooler than I’d like.
Last night I experimented by placing a small plug-in fan inside my bedroom and blew the colder air out into my family room where the heat pump is installed. It seemed to make a dramatic difference at the temperature inside my bedroom. I’m going to test this out/try it for a few more days, and if it continues work, I’ll make a more permanent solution by installing a large CPU fan at the corner of my door and run them using a relay and temperature sensor connected to my home automation system. That way, if the temperature inside my bedroom is colder than the family room the fan will kick on and exchange the air until the temperatures are similar, at which point the fan will turn off.
A Couple More Considerations
Both the inside and outside units of the heat pump make some noise. They’re not excessively noisy, but also not as quiet as a refrigerator (like many folks suggest they are). It’s super important to take this into consideration when placing the outdoor unit. The low hum of the outdoor unit makes is completely livable mounted on the outside of my family room, but most likely would have made it hard to sleep if mounted on the outside of my bedroom. The inside unit can be anything from a low swish, to a moderate level blowing of air depending on what level the fan is set. Most often I leave the fan set on level 2 which provides a noise level I can live with and moves enough air to heat the majority of the house.
Doesn’t blow hot air like a wood/pellet stove. These heat pumps are designed to pump out an 80°F-120°F warm feeling air as opposed to the much hotter 180°F+ that comes from forced air furnaces, and wood and pellets stoves. As the heat pump gets closer to this set temperature it ramps down the temperature of the air it’s blowing out to increase efficiency. This sometimes makes it feel like the heat pump is blowing cold air, when it’s actually blowing slightly warmer air, but it feels cold because it’s lower than our body temperature and blowing.
Hot air likes to travel in straight lines. This heat pump had a very powerful fan that can push heated air easily 30+ feet into the next room, but this same heated air for the most part bypasses my open bedroom door just a few feet to the side of the unit. Additional fans or ways to move heated air around (or a tolerance for colder areas) might be necessary to get the heated air into the rooms off to the side.
Looses efficiency the colder it gets. By their very nature, air to air heat pumps pull heat from the outside air and by changing the pressure/phase of a refrigerant release this heat as warmer air inside the home. As the temperature outside gets colder there is less heat to pull from the cold outside air and the units become less efficient. The Fujitsu units are considered tops with their 27+ SEER and 15+ EER and the best efficiency/coefficient of performance at low temperatures, but they can only go so low. From 0°F and blow performance is significantly reduced, and I found mine to put out very low heat in the -5°F range. At that point I just turn it off and let the radiant slab do what it’s designed to do.
When the heat pump is on it never truly turns itself off. I guess this could be considered a good and a bad thing. It makes the unit far more efficient, because it ramps up and down based on the demand, but for a passive solar house with significant solar gain, this means the unit just coasts along for the entire sunny day even when you need absolutely no heat. I wish there was some circuitry, or way to have the device automatically turn itself completely off if the room temperature is significantly above the set point and increasing. For now, I just look out the window to see if it’s sunny in the morning and turn the heat pump off. I may in the future decide to interface this with my home automation system and use a predictive heat algorithm to determine the most efficient way to heat our home.
Conclusions… so am I happy?
Given everything mentioned above, am I still happy? Would I buy the heat pump again? ABSOLUTELY!
It really is an awesome device, and if it holds up to all the ultra-energy efficiency claims then we are in for saving close to $1000 per year, and paying for the device in less than 3 years with the help of the $300 tax credit and $600 rebate from Maine Public Service. Even better, while receiving all this winter savings, we now have a superefficient, very quiet cooling system in the summer and vastly increased comfort year-round. For me this is the hugest thing, as a quadriplegic who has an impossible time regulating my body temperature, having the ability to quickly heat up/cool down my room will make such an incredible difference in my life!
Before, when I used to get a chill, I’d either close myself in my bedroom and fire up the space heater (because it’s one of the smaller rooms in the house and could increase in temperature more quickly), or run the space heater for several hours in my family room. Now, I can just kick the heat pump on high with my family room door closed to the rest of the house and heat it up 5°F in less than half an hour. Then, once I’m all warmed up I can ramp the unit down, open up to the rest of the house, and keep on saving! And, in the summer, no longer will I be hightailing it to the supermarket or someplace that has air conditioning when it gets too hot. Now, I’ll be able to sit back and enjoy the comfort of my home!