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Old 10-16-11, 11:55 AM   #81
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Quote:
Originally Posted by Xringer View Post
Yeepee, the 2011 Annex 32 Reports are out!
What did you learn?

I did notice this in the second listed report, in section 7 (page 13):

Quote:
In Japan, the design of heat pump air conditioners of single or multi-split type, which are the Japanese standard heating and cooling systems in the moderate climate zone, used to be a simple catalogue method, which led to over dimensioned systems with lower performance in low energy houses.

(emphasis added)
I mention this because I have noticed that you always advise people who are reading your threads to oversize their mini-splits, because the unit will run in reduced capacity when needed.

I think your advice is leading people who might trust you to select less efficient systems, in a similar way to the above quote regarding practices in Japan.

My advice is to do a load analysis, then select a heat pump unit that is slightly smaller than required, and use a secondary heat source under the extreme conditions.

Regards,

-AC_Hacker

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Old 10-16-11, 05:49 PM   #82
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Well, if someone is buying a cooling system for one room, it's pretty easy to find out how many BTUs are required.
Properly Sized Room AC : ENERGY STAR
The information is all over the web..

But, if you try what I'm trying, heating most of the rooms in my house from one central heat source, the old Room Air Conditioners Size rules don't work so well.

IMHO, to get warm air to move by convection, to most of your living areas,
you might need some extra BTUs in reserve..

The best solution would be to install a multi-split with IDUs spread around.

I admit that I do advise people to buy a larger BTUh unit, if the price isn't
is much more than the smaller unit, if the larger unit has the operating range they want, and has similar efficiently.

Let's say the larger unit cost $500 more. With heating oil at around $3.89
this winter, that $500 can buy a single 128 gallon oil fill..
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Old 10-16-11, 10:38 PM   #83
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Quote:
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Let's say the larger unit cost $500 more. With heating oil at around $3.89 this winter, that $500 can buy a single 128 gallon oil fill..
I think the issue is really not about purchase price, but rather the lifetime operation cost.

In general, the larger units use more energy per BTU than smaller units. It is true that prior to variable speed compressors, it was worse than it is now. But the real deal is that a properly sized heat pump will cost less to operate than an over-sized one.

It all starts with knowing what your heat loss is. This can be done by calculating, using a suitable computer program to do the job. Another approach is to use ASHRE Manual-J which calculates heat loss. The computer programs just automate Manual-J. I had pretty good luck with Watts Radiant program called RadiantWorks. It will do a heat loss calc and also calculate radiant floor designs. You would just want to use the first part.

Another way is to use electric heaters with power meters , operating under "design" conditions. And find out how much heat is required to maintain comfortable inside temps.

Most people never do this, and they pay for that oversight for years and years.

The time when bigger was always better is behind us.

_AC_Hacker
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Old 10-17-11, 12:11 AM   #84
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As far as I'm concerned, the time for wasting money on over-priced heating oil is over.
Or, it should be..


So, if you had your house professionally tested and the report said that
you needed 20,000 BTUh..
But, the brand you wanted only came in 18,000 and 24,000 BTUs..

What would most people consider to be the wise choice??

~~~

After living in the north east for over 40 years, and seeing the kind of
winter weather that we've been having during the last few years,
I'm not really all that confident it's not going to start getting
colder during coming years, with longer lasting winters..

Record cold weather roundup – hundreds of new cold and snow records set in the last week | Watts Up With That?

Will Sunspots Freeze Europe This Winter?

CERN - CLOUD: cosmic rays and cloud formation
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Old 10-17-11, 10:42 AM   #85
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Quote:
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...professionally tested... you needed 20,000 BTUh..
But, the brand you wanted only came in 18,000 and 24,000 BTUs..

What would most people consider to be the wise choice??
This is exactly the right question, because it illustrates the difference between sizing for HVAC and sizing for fossil fuel.

(* Regarding "professionally tested", it is a reasonable task for a person to do heat loss calcs themselves if they have the knowledge and tools. Build it Solar has a good on-line heat loss calculator that is based on Manual-J, and as mentioned before other integrated packages (some are free) also have heat loss calcs. *)

In the example you cite, most people would go for the 24,000 BTU heat pump.

But the most efficient heat pump would be 18,000 BTU, with the proviso that secondary heat be available to fill in the heating shortfall on the unusual days (2% of the heating season) when required.

This is the method I have seen on pro HVAC blogs, free on-line design literature, proprietary HVAC design books, etc.

As I have been learning this stuff, and applying it, and since I tend to over-research everything, I used several different pieces of software and compared the results from each and finally I used the real-time testing method of having a bunch of electric heaters with Kill-a-Watts attached to each one (recording the readings every four hours) when the temp got really, unusually cold here a few seasons back. It was pretty handy, because the actual temp outside was the same temp as the design temp in the computer programs. I found that there was some difference between software packages, and I have greatest confidence in the real-time testing method, rather than the calculation methods. But they were all in the ball park.

* * *

Fossil fuel furnace & boiler sizing is not done this way. The correct way for fossil fuel is to go a bit over the minimum required heating. In fact, I have seen some of the older software for fossil fuel boilers that has a +50% sizing factor built in to the software! The basis of this thinking is that the installers want to avoid call-backs.


Regards,

-AC_Hacker
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Old 10-17-11, 07:10 PM   #86
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Quote:
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In the example you cite, most people would go for the 24,000 BTU heat pump.

But the most efficient heat pump would be 18,000 BTU, with the proviso that secondary heat be available to fill in the heating shortfall on the unusual days (2% of the heating season) when required.

In my case, the back-up heat is going to be much more expensive than using the primary (Sanyo).
Heating oil could cost us 4 to 5 times as much. Maybe more!

Heating oil prices spike

If we can get away using our 1200w ceramic & 1200w Oil-filled heaters, it's not going to be too awful.

That 2% of the season, you are talking about could become a larger number when you
start taking the age of the people being warmed into consideration.
I'm getting so creaky, that I feel cold when it's actually warm in here..
Right now, I'm wearing my Old Navy hoodie, like it's winter time,
and it's still 74.5F in this room!!

If a worse case scenario, happens and we get a few weeks of less than 10 deg F weather,
We might end up visiting the city library for hours a day,
where city employees keep the temperature in the mid 80s..

Anyways, I'm becoming distrustful of weather forecasters.
I'm getting a feeling that winters in this area, are going to get a lot worse,
before they start getting mild again.
(Hence the larger and more powerful snow thrower)..
Don't worry, it's more fuel efficient.
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Old 10-17-11, 09:23 PM   #87
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Heating Oil Usage in the US: How Much is “Average”? | HeatingOil.com

"According to a 2005 report from the Residential Energy Consumption Survey (RECS),
the typical home in Maine uses 850 to 900 gallons of oil per year; in New Hampshire, 800 gallons."

Wow, at today's prices, 800 gallons is about 3,000 bucks.
One could by some nice mini-split hardware with that kind of mola..

LG3HV27S
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Old 10-18-11, 12:11 PM   #88
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Quote:
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In my case, the back-up heat is going to be much more expensive than using the primary (Sanyo).
Heating oil could cost us 4 to 5 times as much. Maybe more!
But we're talking about 2% conditions.

Quote:
Originally Posted by Xringer View Post
That 2% of the season, you are talking about could become a larger number when you start taking the age of the people being warmed into consideration. I'm getting so creaky, that I feel cold when it's actually warm in here.. Right now, I'm wearing my Old Navy hoodie, like it's winter time, and it's still 74.5F in this room!!

From what you are saying, it sounds like you are exactly describing the way it feels to live in a poorly insulated house... like on a really cold winter day, to sit right next to a single pane window... that chill that you feel on your skin. It's the loss of radiant heat from your body that gives you the chill feeling. If you were to go to triple pane, there would be no chill feeling.

If your house is really well insulated, you can feel comfortable at a lower temperature.

Insulate, insulate, insulate.

-AC_Hacker
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Old 10-18-11, 12:22 PM   #89
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It's 72 in here now, but down at the floor, it's cooler.. 70 LOL!!

No drafts in here today. Any moving air is coming from a Sanyo and it's warm!

I'm just more sensitive to the cold these days. Part of it has to do with my BP meds.
It makes your extremities feel colder, for some reason.

I have been keeping the house at 21C today, while I'm trying to figure out how
to see how well the old Andersen thermopane windows in the den are working.
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Old 10-18-11, 02:33 PM   #90
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Quote:
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I'm just more sensitive to the cold these days. Part of it has to do with my BP meds.
Sorry 'bout your meds.

The topic of discussion is the reduction in heat pump efficiency that results from over-sizing a system.

-AC_Hacker

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