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Old 02-21-13, 07:06 AM   #21
Xringer
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A lot of homes have attached decks in the back.
If it's shaded under there and some kind of rain shield can be installed, that might be a good place..
I don't think the specs for over-head obstructions/blockage/snow roof are critical at all.
If there is over a foot of over-head space and good air flow gap (+18") on the sides,
there shouldn't be a problem with intake air flow..

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Last edited by Xringer; 02-21-13 at 07:17 AM..
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Old 02-21-13, 10:50 AM   #22
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Quote:
Originally Posted by basjoos View Post
I'm getting ready to install a Mitsubishi 2-zone mini-split and decided to mount the outside unit on a small platform outside the second floor on the north side of the house.
I've had the mini split that I installed running for three winters, so I've had time to think it over.

I've read your considerations, and they are all sound.

I would repeat what has already been said about NOT mounting your outdoor unit to the house. One of the miracles of the mini split is how unobtrusive they are... so any noise that you hear from one will, over time, seem intolerable. The compressor in the mini split is variable frequency, so as it goes through it's various RPMs, any part of the structure of your house that is capable of being resonant with the compressor at that time, will resonate and create an intensified sound... in the long term, you will not be happy. So if you do build an elevated structure for your OD unit, don't even tie it to your house... resonance will be transmitted.

(* anchoring to a concrete pad, not attached to your house is actually a very good idea *)

The amount of length permitted in a lineset is fairly long, so if you were able to shave 8 or 10 feet, there's not really a big gain.

The idea of putting the OD unit in a carport type of space is just great, for all the reasons mentioned.

And another thing that might not have been mentioned, is the temperature of the very large quantities of air that get expelled from the OD unit. In cold weather, this air will be much colder than the ambient air temperature, in hot weather, it will be much hotter than ambient air temperature. So, if you like to entertain a lot, you wouldn't want that air being ejected into your outdoor entertainment area... nor in the area near your most frequently accessed entrance to your home.

Best,

-AC
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Old 02-21-13, 08:03 PM   #23
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I am going to drift off topic, I am trying to talk myself into buying a mini-split.



Question #1
If Its real cold outside say 2 degrees Below freezing a heat pump may make less heat per watt,compared to electric baseboard heat.

true or false?

Question #2

If I have cold weather should I buy highest BTU heat pump I can afford. The Premise is - I want one sized not for ideal conditions but for my winter heating season conditions.
Who wants a heat pump that only puts out 12000BTU's on a warmish day.
On a cold day it will make what 1/2 that ?

Question #3
How do they rate heat pumps ? as in outside temperature for a Giving BTU output ?
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Old 02-21-13, 08:55 PM   #24
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#1. At 30def F, my Sanyos doesn't really see that as being very cold..
Sanyos will perform very well down into much lower temps.
See chart. http://i46.photobucket.com/albums/f1...CL/heatcap.jpg

At around 25F(-3.9C) seems easy for the Sanyos, under 20F(-6.66C)
they start to work harder. But when it's 5F (-15C) they will still
put out more heat than electric baseboard heat (Using the same wattage).
But, when you go lower than -10 or -15C the top-end BTUh falls off.
The chart shows the dead end is around 16,000 BTUh..
So, at that point you might want back-up heat.. (electric baseboard )?
Depending on your load (and insulation/sealing etc).

#2. Wow, that's a good question. I'm using a 36,000 BTUh heater in a smallish Den,
and it's way too large for the room.. But it works great. Because the Sanyo Inverter
allows it to lower the RPMs of the two large motors in the outdoor unit.
That means the BTUh is very adjustable, between 4,400 & 29,000 BTUh..
That uses 290watts to 2.49 kW per the chart,
but it's actually about 420 to 480 watts on the low end (in my house).
I think the 290w might be seen, if you are heating on a very mild day..
http://i46.photobucket.com/albums/f1...L/poweruse.jpg

Because the system is 'too large' for the sq footage it's heating (the load),
it's not working very hard. It might last a few years longer than normal.?.

If it doesn't cost a much more for a larger unit than you really "need",
and the power specs are good.. Why not get the larger unit?
I know a few folks that went larger and are very happy they did..
It allows for fast heating of a cold house and those cooling extra BTUs
BTUs come in real handy on those freak summer days when it's super hot.


#3. Inside and outdoor temps dictate power usage. See chart.
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Old 02-22-13, 12:00 AM   #25
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Thanks, that was very helpful.
I found from the chart you posted that A 29,000Btu mini split(with the same components)
would produce 22,420Btu's or 30% less heat (then its rating) on a 23F or -5c day.

It rarely goes below 23F or -5c Where I live, So I could use a unit with about 30% more Capacity then I really need. That should do it.

I could figure out my current use in electricity over the coldest months, convert that to Btu's and size the Mini split accordingly.

And its true rating is for a 43F or 6.1c day @ 29,000Btu's
&
On a warm day 63F or 17.2c it would make 34,000Btu's

Everything points to getting a unit.
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Old 02-22-13, 12:21 AM   #26
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I think I can size the heat pump by using my current baseboard heater load.
Also having 3 smaller indoor units hooked to a big outdoor unit would work for me.

So say a 29,000 outdoor unit and 3 12,000btu indoor units.
A 1000 Watt Baseboard Heater is about 3,400Btu's

My living room has 2 1500watt baseboards or 10200 Btu's
Each of the 2 upstairs bedrooms has a 1500 watt heater or a 5100Btu's
My rec room Downstairs Has a 1500w baseboard as well. (don't use it)
So that's 25500Btu. So one 29,000Btu Heat Pump should heat my whole house.

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Old 02-22-13, 05:48 AM   #27
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For some reason the manufacturers don't seem to want to give Americans real data about performance. Maybe we are not trained enough to understand it but in Europe that info is front and centre. The standard there is to measure performance at a given air entering temp and water leaving temp.
In the one below they quote the standard of A2W35C and A2W55C to give your COPs.

Other manufacturers I have seen give the data at A-7W35 as well as at 2C. There is a lot more info in that number than we get especially if we have 2 numbers than we can make an output graph.
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Old 02-22-13, 07:01 AM   #28
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Sounds like you have the sizing done.
Keep in mind, those Sanyo spec is for an older model. You might be able to
get much better performance from newer hardware.

Heat from a source downstairs will flow up the stairs, but cooling upstairs will be a real problem.

If you use a single unit in your living room, think of it as working like
a wood stove in the same location. Will that heat your whole house?
Mine did, but it wasn't really super warm in the back bedrooms..
Nice for sleeping, but I wouldn't want to sit in there to read a book..
I would head for the warmer rooms..

One other thing to consider is the humidity/dewpoint on days when it's between 20&30F.
That will cause(& cost) you some defrost cycles. You might want to find out if anyone
in your area is using ASHPs for heating and find out about their performance.

When the dew point is running at the same temp as the air temp, it will cause defrosts.
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Old 02-22-13, 07:05 AM   #29
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Quote:
Originally Posted by ecomodded View Post
Thanks, that was very helpful.
I found from the chart you posted that A 29,000Btu mini split(with the same components)
would produce 22,420Btu's or 30% less heat (then its rating) on a 23F or -5c day.

It rarely goes below 23F or -5c Where I live, So I could use a unit with about 30% more Capacity then I really need. That should do it.

I could figure out my current use in electricity over the coldest months, convert that to Btu's and size the Mini split accordingly.

And its true rating is for a 43F or 6.1c day @ 29,000Btu's
&
On a warm day 63F or 17.2c it would make 34,000Btu's

Everything points to getting a unit.
Use ahridirectory.org and look up the unit you are looking for in the directory under the Variable-Speed Mini-Split and Multi-Split Heat Pumps section, you can see its 17F rating. Since you don't get that cold you could match your load to that. If you don't have another source of auxiliary heat for the absolute coldest nights, you might want to step up slightly on your load requirement to account for defrost cycles which will cause the unit to temporarily stop producing heat. Also from the AHRI site, higher HSPF numbers are more efficient units. I'm not sure if SEER or EER are terms used in Canada but higher values for those are better for cooling efficiency during the summer.
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Old 02-22-13, 08:30 PM   #30
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Quote:
Originally Posted by MN Renovator View Post
Use ahridirectory.org and look up the unit you are looking for in the directory under the Variable-Speed Mini-Split and Multi-Split Heat Pumps section, you can see its 17F rating. Since you don't get that cold you could match your load to that. If you don't have another source of auxiliary heat for the absolute coldest nights, you might want to step up slightly on your load requirement to account for defrost cycles which will cause the unit to temporarily stop producing heat. Also from the AHRI site, higher HSPF numbers are more efficient units. I'm not sure if SEER or EER are terms used in Canada but higher values for those are better for cooling efficiency during the summer.
We use the same system you do and almost all the equipment sold in the US is also sold in Canada. When I am looking for the most efficient product I can find, I go where most of the efficient stuff comes from......typically Germany or Denmark or Austria (sometimes others, including the USA). I find they are more truthful about ratings than we get over here. Take car efficiency for example. If some company says their SUX2000 gets 50mpg, do you believe them? I've never seen a North American vehicle meet the advertised target.

On the other hand, I brought over a 15 year old 1 ton VW truck from Germany. The "passport" (as they call it) states that it gets 9.5L/100km combined fuel consumption. And it did.

In my trade, every advance in heating efficiency comes from Europe. Every company here that makes a similar product, bought parts or technology from Europe.

Anyway, the HSPF numbers are good for comparison with other like products but I think the way I presented it above is more honest and has more real info even though the AHRI has data shown. The home owner has to be smart enough to understand it though, and I don't think the average North American gets taught to understand these things, unfortunately. Just my 2cents.


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