I thought I would share my experience with you.
I live an a 1920's stucco Tudor in Minneapolis. The house has been updated with insulated windows and celulose blown in the walls, but it still isn't and can't be (without massive remodel) tightened up the way a modern house can be.
I have an older forced air furnace in the basement and central air which rarely gets used.
The house is a 1.5 story with a master bedroom and office on the second floor. The second floor has been the problem. This area gets poor airflow from the furnace and often experiences extremes of heat in the summer and cold in the winter.
In October I purchased an Amcor Air mini split inverter heat pump (12000 btu cool, 15,000 heat) from Kingerson's online.
http://www.minisplitacunit.com/12000....html#features
As you can see like many inverter units the specs were impressive. Living in Minneapolis I was most concerned with the heat output and cost of operation.
Here's what I can tell you after 3 months of use and a couple of utility bills and some really cold weather....
The unit functions GREAT as a supplemental heat source, and GREAT as a massive air conditioner.
The specs on mine state that it is a SEER 20 with a HSPF of 10.1
The operating temperature range (outdoor) for heating goes as low as -4 degrees (F)!!
My unit was 90% installed by me. I needed an impact drill (rented at Home Depot) to make a hole for the wires and pipes. I mounted the unit on the wall, and ran the pipes down the outside wall to the compressor which is mounted on my cement patio. I hid the wires and pipes inside of a rain gutter and it is hardly noticable by anyone who isn't specificly looking for it. I ran an ad on craigslist for an HVAC man to help me set it up and double check my work. I found a great guy who even re-did my flare fittings with a special gooey thread compound instead of the teflon I used. He then vacuum'd the lines and tested it out. I have him $120 for 90 minutes of work and we were done. The electrical hook up was a simple 120v affair and the wiring was simple. The manual sucked, but it wasn't rocket science.
I had good experience with Amcor customer service and shipping as well. The Energy Guide Sticker stated it was only a SEER 19; so I called to ask about the descrepency. They were great, and told me that they made up the stickers before getting the results back from testing. The unit did better than they thought. He offered to send a new sticker, but I didn't really care. I was just happy that the service was competent and friendly (and fluent in English).
The unit cost about $1200 and was delivered to my door step in 3 large cardboard boxes. Total cost for unit plus equipment rental, electrical stuff and HVAC guy was under $1500. I'll post photos of the install if anyone is interested.
So far, I got to test it in some 80 degree (outdoor) weather in October. The A/C works incredibly well. It is not only far quieter than the noisy window units, it moves much more air at much greater velocity. In late afternoon, the second floor receives direct southern sun on the roof and knee-walls which are only insulated with 3.5" of celulose. Often the temps can reach into the 90's indoor without A/C. This unit can cool the area in about 10 minutes under the worst of circumstances. The area is about 600 sq ft.
In December we got a string of sub-zero days. I was really curious to see how the heat pump would work. Normally we turn the temp inside down to about 64 degrees at night and I pump it up to 75 degrees during the day (I work in a home office at the other end of the floor, and keeping it hot helps make sure the heat reaches all the way back to my office).
Here's what I found regarding the heat output.
1. The unit puts out good heat (at least 80% of max capacity) until outdoor temps drop to about +5 degrees (F). Below that the temperature of the air coming out begins to drop. Higher fan settings just blow more 'less hot' air.
2. The unit shuts itself off when it is too cold to generate usable heat. This temp seems to change with relative humidity. While it is certainly 'dry' by our standards in the freezing cold winter of Minnesota, the relative humidity may create a dew-point that is not too far below the ambient outside temperature. When the outdoor compressor unit is running (even when it is cold outside) you can put your hand in front of the fan and feel that the escaping air is even colder than the outside ambient air. Even when it is only 10 degrees outside you can still feel that difference, which is pretty amazing. With a dew point close to ambient outdoor temperature this can also cause ice or frost on the coils, causing a defrost cycle. Eventually the unit is doing too much defrosting and it just shuts off completely until it can efficiently start back up again.
This is key, and I couldn't get an answer about this before I bought. I was worried about the heat pump chugging inefficiently along all night burning electricity on a permanent defrost cycle if I left it on some night and outdoor temps really dropped. The good news is that it is smart enough to shut itself off!
3. The outdoor unit is inverter-run, and you can tell because the fan and the compressor change speeds. Its pretty cool to watch. The indoor unit, however, is an AC motor fan. It runs at one of 3 speeds. I wish it also changed dynamically as a variable speed fan, but it doesn't. Still- it works fine and is a major improvement over a window unit.
4.Bills: In October I couldn't even tell that we were running it. It is probably at least 200% more efficient than the window units, and much larger capacity- so it didn't need to work real hard. The bill increase was not discernable, even though we ran the fan every night. I expect that will save some serious electricity next summer.
In December my electricity bill was about $145. With no HVAC or other seasonal loads I expect this number to be around $70. We pay about .10 kwh here. I haven't gotten a chance to log in to the power company's website to compare actual usage, but I'm very happy with it.
An added benefit is that when our outdoor temps are a little more 'moderate' (average winter temp is +20 degrees) and the heat pump is producing at full capacity I put a fan at the top of the stairs and blow hot air down to the first floor. This keeps my gas furnace from turning on as often. My gas bill in december dropped about $30 (from same time last year). Not much, but I also like to consider that I am essentially conditioning an extra 600 sq ft that wasn't really being conditioned before. If the house was properly ducted and the gas furnace could reliably heat it I'd estimate that my gas bill would increase by about $100.
Net savings isn't enormous, but the moderate savings coupled with much more comfortable square footage has been great.
Final Thoughts:
I think this is a game-changing technology for three reasons:
1. Low cost for a unit (bought over internet) coupled with simple install that can be 90% DIY can keep costs LOW.
2. Many people in older homes need fairly radical remodeling work done if they replace furnaces or boilers- which is why there are so many older homes in cities with 30 year old inefficient 60-80% aflue units around. A Mini split allows you to keep them running, but supplements their heat with something very efficient. Hopefully you are only using inefficient heat on the coldest days.... in my mind that's a reasonable compromise. Also adding decent A/C to houses with radiant heat (radiators) is wonderful.
3. It is simply amazing to me that I can use an air source heat pump with better efficiency (HSPF 10.1) than almost any ground source heat pump out there (without the expense and engineering of digging up your yard), and it will work in 95% of the temperatures I am exposed to (even here in Mpls), for
1/20th the cost!!
My last two ideas:
- start putting this technology in all HVAC and refrideration units. The difference in efficiency is just too large, and the technology is not all that complex. Imagine if homes in the future had one large really efficient heat pump compressor outside. It fed anything that needed heating or cooling. Small minisplit units in the rooms, and units in refridgerators and freezers. All having their heat efficiently moved around from where its needed to where it isn't.
-an air source heat pump could be made into a cheap gound sourcer with this technique:
PVC "earth tubes" are laid underground to warm ambient air up to a range that works for an air source heat pump. Simply run several of them in a shallow trench for 40-50 feet and have them exit in a manifold around the outdoor compressor. They would warm ambient outdoor air temp slightly. It wouldn't take much to increase temperatures below zero temps to +5 degrees. Since these earth tubes don't enter the conditioned space of the home, you don't need to worry much about condensation or mold or permits. They would increase efficiency by cooling air in the summer as well. Here's a link to a story about someone who did it with an older air source heat pump in Nebraska:
Earthtoys - Emagazine
I'd like to hear other people's experiences if they try these out.
Thanks for the discussion-
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