Back Up Heat Source and Boosting Loop Temps

[AC_Hacker]

Originally Posted by stevehull

AC,

I lived up north in that area. It is cold. That area of IL is also very cloudy and windy (see page 1, post 1) in the winter. Simply stated, 9000 BTU/hr is not going to cut it at 0F in that climate even with a 1000 sq. ft home and average R30. Twenty five years of work allows me to guess - and that's what I did.

24,000 - 30,000 BTU/hr to get a delta t of 70F in that climate and with those conditions.

It is physics.

Steve

Well, I don't know if I'd call your method 'physics'. I think a heuristic based hunch might be a better term... and more difficult for most people to critique.

And don't get me wrong, because a quarter century of experience consulting in geothermal heating/cooling & rational energy use has got to be worth something, and who knows... you may even be right.

But I just don't think that your approach is very interesting.

So I have been looking for a more interesting approach to this problem...

So here's what we know:

• gas bill for the period of 12/20/2013 - 1/22/2014
• 72.42 therms used during that period
• Location: Woodstock, IL

Here's what he wants to know

• Size of GSHP

First off we can convert the Therms of Nat Gas to BTUs, so assuming 90% efficient furnace, that would be 6,516,244 BTU for that billing period.

So I went to my FAVORITE Degree Day site and got daily HDD data for Midtown, Woodstock, IL, USA, for a time period that included his gas bill. I used 68F as the base temperature. Bear in mind that this is daily data measured at his location during the period of his gas bill. This is what I think physics looks like.

Description:,"Fahrenheit-based heating degree days for a base temperature of 68F"
Source:,"www.degreedays.net (using temperature data from www.wunderground.com)"
Accuracy:,"No problems detected"
Station:,"Midtown, Woodstock, IL, US (88.45W,42.32N)"
Station ID:,"KILWOODS3"

Date,HDD
2013-12-20,38
2013-12-21,40
2013-12-22,42
2013-12-23,60
2013-12-24,66
2013-12-25,47
2013-12-26,46
2013-12-27,38
2013-12-28,31
2013-12-29,44
2013-12-30,68
2013-12-31,64
2014-01-01,56
2014-01-02,60
2014-01-03,62
2014-01-04,43
2014-01-05,59
2014-01-06,82
2014-01-07,75
2014-01-08,68
2014-01-09,66
2014-01-10,36
2014-01-11,35
2014-01-12,34
2014-01-13,33
2014-01-14,42
2014-01-15,54
2014-01-16,43
2014-01-17,55
2014-01-18,56
2014-01-19,46
2014-01-20,41
2014-01-21,67
2014-01-22,63

The first thing I did with the data was to graph it out to see what the numbers looked like...

Well, no major revelations here, but those Heating Degree Days sure do jump around a lot in Woodstock, IL.

Next, I added up all the degree days and found what percent of the total each days data represented. Then from that calculated data, I found out how many BTU/day worth of natural gas would have been consumed each day (assuming 90% efficient gas furnace). Lastly I looked at the average BTUs generated each day (more HDD, more nat gas).

So, it is the rightmost column that I find to be particularly interesting, because it is what his furnace was actually putting out on average per hour during the Arctic Vortex that we all know and love so well.

So, it looks to me that if one were to choose a GSHP system that is just slightly smaller than the maximum required, a 12,000 BTU/hr would be an intelligent choice, with some kind of auxiliary system to fill in the gap.

There will be daily differences that this method does not capture, but I think it has considerable merit in sizing a GSHP, especially considering the cost of earth work, and how a seat of the pants guess could be the difference between a $20,000 system and a $50,000 system.

As a final note, I think that this method should be applied to a wider time frame, as I did see one HDD from an earlier date that should, itself be chosen as the maximum data point. That particular outlier HDD make all of these high HDD values shown above relevant, and none are outliers.

Best,

-AC_Hacker

[AC_Hacker]

Originally Posted by MN Renovator

It's 15kWh per square meter...

I think you missed it again...

Can you see the difference now?

-AC

[MN Renovator]

Originally Posted by AC_Hacker

I think you missed it again...

Can you see the difference now?

-AC

No, I don't think I did.

"annual heating demand as calculated with the Passivhaus Planning Package of not more than 15 kWh/m² per year (4746 btu/ft² per year) in heating and 15 kWh/m² per year cooling energy OR to be designed with a peak heat load of 10W/m²"

15kwh/square meter per year. It's right there!

[AC_Hacker]

Originally Posted by MN Renovator

... (4746 btu/ft² per year) ...

OK, do you realize that it means that your energy budget for the year is 4746 BTU/sq foot?

2100 sq ft * 4750 = 9,975,000 BTU per year

So that means that your hourly heating budget is 1139 BTU/hr.

So, what exactly is your problem with that?

-AC

[MN Renovator]

I never said I had a problem with that. I'm not sure where you gathered that I did. I just had an issue with the fact that you were ignoring that there is an OR in there, allowing for "OR to be designed with a peak heat load of 10W/m²(3.17 btu/h.ft² per hour)" instead.

"Even some of these requirements may not be actually be mandatory: in a 2008 interview in Energy Design Update. Dr Wolfgang Feist himself stated that the heating demand number could be anything[referencing total heating & cooling demand of <15 kWh/m2/yr]. In this interview Feist also stated “As long as you build a house in a way that you can use the ventilation system … to provide heating and cooling it can be considered a Passivhaus.”

Energy Design Update. “An Interview with Wolfgang Feist” Aspen Publishers, Vol. 28, No. 1, January 2008.

There are many Passivhaus homes that are built without using the ventilation system as their heating source, its not technically required but his point was the total heating demand number isn't mandated. There's an OR in there.

This better describes that.
BSI-025: The Passive House (Passivhaus) Standard

[AC_Hacker]

"E=MN Renovator;35613]I never said I had a problem with that...

BSI-025: The Passive House (Passivhaus) Standard[/QUOTE]

Even some of these requirements may not be actually be mandatory: in a 2008 interview in Energy Design Update1 Feist himself stated that the heating demand number could be anything. In this interview Feist also stated “As long as you build a house in a way that you can use the ventilation system … to provide heating and cooling it can be considered a Passivhaus.” By this latter definition, thousands of Building America homes that use the heating and cooling system to provide ventilation, are Passiv Hauses! Of course, if the requirement is for a non-recirculating heating system then this is quite restrictive and not very beneficial for cold climate housing.

I think that this article that you keep pointing me to is actually an exercise in carefully worded dis-understanding. In other words, the author understands the basis of the Passive House concept and is constructing his argument to craft misunderstanding in the mind of the reader.

I'm much more interested in the fact that Passive Houses actually work, and that the basic principles are fairly easily accessible and that the fine points of construction are also available, though not so readily accessible. Even the design software is an amazing bargain.

But regarding the passive house idea, do you actually have a point that is interesting and useful?

* * *

This conversation reminds me of a friend who had a very serious cholesterol problem, that made him a prime candidate for a heart attack.

I showed him a film that was based on a very famous study on diet and disease in China. The upshot of the study was that there was a direct link between meat consumption and cancer and also heart and arterial disease and cholesterol.

He seized on the idea but he did find a tiny loop hole in the film where it said that greater that 15% meat consumption could be the trigger point for cancer. Whereupon, he sat down and did some calculations to figure out exactly how many hamburgers he could eat per week... when the point of the study was that meat and all animal protein in general, without regard to if it is 'organic ' or not, should be eliminated from the diet.

So, his cholesterol problems continue on...

* * *

In the studies of Passive Houses I have seen, the upshot was that total energy use had been reduced by a factor of 10, compared to a "code house".

Maybe that is an easier idea for you.

How are you doing by that measure?

-AC

BTW:

In 2008 the European Union passed a resolution calling on each European member state to adopt the Passive House Standard by 2016 for all new construction and major renovation projects. Ultimately this resolution will alter the construction industry in all parts of Europe, as the continent recognizes the need to build for long-term economic benefits, improved indoor air quality and personal and national energy security.

It's good to see that somebody is getting the message.

[wewantutopia]

WOW, I was gone for the weekend and this thread blew up!!

I got your email AC Hacker but I don't have enough posts yet to respond. I do see, however, that you found that I already posted the data you were asking about.

Thank you so much for running those numbers!! It is very interesting to see! I'm pretty happy about the high number of ~12600 btu per hour. That was one COLD day/night -4 hi/-17 low with 40 mph winds. Of course it could be much better. Eventually new windows will help a lot. I still have 2 basement walls left to do with exterior XPS (which includes fixing the mortar in the block part of the wall. They are VERY leaky so the reduced infiltration will also help a LOT).

I should add that really the house is 1500 sq ft including the conditioned basement. I'm so used to calling it a 1000 sq ft house since the basement doesn't count as living space for real estate purposes. It really IS used as living space though.

My stating that it is just under PassivHaus standards was just based on what I've read the insulation rvalues used are. I never did a btu/sq ft/year analysis. In reality I see we're no where close; but, at about 5 or 6x above the high standard (with room for improvement) I'm pretty happy.

[AC_Hacker]

Originally Posted by wewantutopia

...I got your email AC Hacker but I don't have enough posts yet to respond. I do see, however, that you found that I already posted the data you were asking about.

Thanks... It was fun to work out.

I don't know about the world of heating, but it was certainly breaking new ground for me.

I was amazed that, given just a few bits of information, it was possible to do a moderately detailed analysis of a house in an area, neither of which I had ever seen.

And the difference in stated floor area really doesn't matter to the analysis, because the 'real' area was included in your gas bill!

If you could find out what the recorded temperatures were during that period, it would be very useful to combine them with the other data.

I just guessed that 90% was the rated efficiency was of your gas furnace. If my guess was wrong, that would make a difference to my model. It would be very easy to change, just tell me the rated value and I will make the changes accordingly.

Those Heating Degree Days sure are powerful numbers!

But, seriously your energy consumption during the Vortex was very respectably low. Congratulations on your good work!

Best,

-AC

[AC_Hacker]

Originally Posted by MN Renovator

Let's take my house for example with the 4,750BTU/sf/year standard.

2100 sq ft * 4750 = 9,975,000 BTU per year.
Electric resistive heat - 2924kwh
3 COP heat pump - 975kwh
96.2% condensing natural gas furnace(40k is way oversized but just for the numbers) - 104 therms

You need to apply heat. Solar gains are great but they aren't available at night and the passivhaus standard doesn't require(and actually many don't) have solar heating beyond their glazing or high-mass. Granted a solar storage tank with a few solar water heating panels will help for most of the winter but a system sized to carry the multiple cloudy Minnesota weeks we get here to cover the heat load gets huge and very expensive. PV and a mini-split is about the best way to mitigate those periods IMHO if the goal is to not net-source the energy externally. A net-zero home is fairly easy with enough PV and mini-split heat with passivhaus standard building methods.

Please read these two links and maybe you'll better understand where I'm coming from:
Passivhaus Buildings Don't Heat Themselves
BSI-025: The Passive House (Passivhaus) Standard

FWIW, I think I'll be about 2/3 towards the passivhaus heating goal with my retrofit once it is finished.

I came across a very interesting article over at Build It Solar that details how a guy took an existing uninsulated brick school house and attempted to convert it to comply with Passive House standards.

Here's some info on his location:

Kingston, Ontario at a latitude of 44 deg. N. This is a 7150 F. degree-day heating climate with an extreme winter ‘Design Day’ temperature of –5.8F.

I thought you'd be intrigues by his naive audacity at trying to convert an unsulated brick building to a Passive House.

I don't remember if your HDD is similar to 7150 F, or not.

Best,

-AC

[AC_Hacker]

Originally Posted by MN Renovator

Let's take my house for example with the 4,750BTU/sf/year standard.

2100 sq ft * 4750 = 9,975,000 BTU per year.
Electric resistive heat - 2924kwh
3 COP heat pump - 975kwh
96.2% condensing natural gas furnace(40k is way oversized but just for the numbers) - 104 therms

You need to apply heat. Solar gains are great but they aren't available at night and the passivhaus standard doesn't require(and actually many don't) have solar heating beyond their glazing or high-mass. Granted a solar storage tank with a few solar water heating panels will help for most of the winter but a system sized to carry the multiple cloudy Minnesota weeks we get here to cover the heat load gets huge and very expensive. PV and a mini-split is about the best way to mitigate those periods IMHO if the goal is to not net-source the energy externally. A net-zero home is fairly easy with enough PV and mini-split heat with passivhaus standard building methods.

Please read these two links and maybe you'll better understand where I'm coming from:
Passivhaus Buildings Don't Heat Themselves
BSI-025: The Passive House (Passivhaus) Standard

FWIW, I think I'll be about 2/3 towards the passivhaus heating goal with my retrofit once it is finished.

I came across a very interesting article over at Build It Solar that details how a guy took an existing uninsulated brick school house and attempted to convert it to comply with Passive House standards.

Here's some info on his location:

Kingston, Ontario at a latitude of 44 deg. N. This is a 7150 F. degree-day heating climate with an extreme winter ‘Design Day’ temperature of –5.8F.

I thought you'd be intrigued by his naive audacity at trying to convert an uninsulated brick building to a Passive House.

I don't remember if your HDD is similar to 7150 F, or not.

Best,

-AC