Back Up Heat Source and Boosting Loop Temps - Page 5

MN Renovator · 02-07-14, 11:47 PM

The Passivhaus standard is a bit strange but keep in mind that the passivhaus standard has an OR in there.

"The specific heat load for the heating source at design temperature is recommended, but not required, to be less than 10 W/m² (3.17 btu/h.ft² per hour)."

This allows my heat load of my 2100 sq ft house to be 6657BTUhr(my design temp is -11f or -13f depending on where I look). Now in his 1000 sq ft bungalow that would be 3170 BTUhr at design temp. A question that I've never seen the answer to is how the design load in Germany is derived. In the US, design temp is the point where it warmer than that temp 99% of the time(or colder 1% of the time depending on how you look at it). 1% of a 8760 hour year is 87.6 hours. What standard does Germany use, is it ASHRAE? Either way, I'm sure the design temps aren't far off but that's just an aside.

For my house, to get to 6657BTUhr at design temp, I need the absolute best U-value .11 windows(R9), R100 in the ceiling, R45 walls, and to not lose much through the basement. Of course passivhaus ignores the temperature that an area reaches. If my design temp was 15 degrees, I'd be okay with R35 walls, R60 ceilings, and a much more affordable U-value .2 windows (R5). Instead of going passivhaus, I'm willing to use those numbers to get to just under 10k design load. 4 inches of rigid foam makes life easier and I'm content with a heating bill consisting of about $40 of natural gas or cutting the $210 of natural gas connection fees and moving things to mini-split electric. Sure my winter months will cost more but there will be a good savings by not paying the connection fee.

Now with a GSHP, taking a look at an example manufacturer, how about the biggest one Waterfurnace. Their smallest unit isn't even offered with an ECM motor so the efficiency is a bit lower but with the low load I think it is good enough. Fans law indicates to us that lower air flow is less power needed. Their 5 series model 012 unit at 4gpm flow and 400 CFM airflow provides 14,500BTUhr cooling at 59 degrees entering water temp with 25.5EER and 12,300 heating with 50 degree entering water temp and 4.5 COP. If you've got an R30 wall, R80 attic, etc. 1000 sq ft bungalow that needs more than 12,300BTUhr heating, you need to work on the infiltration losses.

AC_Hacker · 02-08-14, 01:36 AM

Quote:

Originally Posted by MN Renovator

The Passivhaus standard is a bit strange but keep in mind that the passivhaus standard has an OR in there.

I got my Passive House heat loss load at THIS URL.

Where it states: "Annual heat requirement ≤ 15 kWh/m2/year (4.75 kBtu/sf/yr)"

This is total BTUs per year... not 4.75 kBTU/hr per year.

Passive Houses do utilize passive solar when possible.

But 4.75 kBtu/sf/yr is the definition of the passive house. A Passive House that can meet the standard in Southern California would obviously not work in Indiana, it would need to be built different to achieve 4.75 kBtu/sf/yr.

It is a very stringent standard.

A house that can meet 4.75 kBtu/sf/yr does not require a heating system.

It's a revolutionary concept.

It takes a while to wrap your head around it.

-AC

Mikesolar · 02-08-14, 08:19 AM

Quote:

Originally Posted by jeff5may

I grabbed the illustration from the website of:

TechniSolve Software

They have a whole suite of programs for whatever (air or water) heating, cooling or refrigeration solution you'd like to simulate. Not cheap.

The illustration breaks down a freeze-frame in time of a running phase change system. It appears this one is something like a walk-in refrigerator. All relevant temperatures, pressures, heat flows, and mass flow are recorded for respective devices.

The long and short of this system is this: the evaporator absorbs 163.1 kw from its environment and the compressor uses 39.1 kw to pump refrigerant, yielding 202.2 kw of heat rejected by the condenser. Since the unit is in cooling mode, COP is the ratio of heat absorbed by the evaporator divided by compressor power, or 163.1/39.1 or 4.17. If the unit was used as a heater, the COP would be higher at 202.2/39.1 or 5.17.

I know of TechniSolve but didn't want to spend the bucks to get it. Instead, I have started to learn CoolPack which is a free download from Denmark. I haven't been using it for a year so I have probably got rusty.

jeff5may · 02-08-14, 10:52 AM

I tried a demo of the Technisolve software for a few days before i knew about coolpack. It is kind of like the autodesk/autocad software scheme: they have a plethora of modules that are each built for a specific purpose. If you are designing boilers, they have a different module that works well for that. If you are doing a heat pump, they have a condenser designer module that does the same basic thing. The thing I liked best about it was the wide variety of refrigerants in the database to select from.

Coolpack, otoh, is very compact and generic in nature. To me, it is easier to use, since you don't have to learn five or six modules of software to put together a simulation. Once you learn two or three modules, that's about it. However, you usually have to look up your own data for accurate representation of components. Luckily, the mfr's post up thorough data on their products at ASHRAE conditions on their spec pages. Sometimes you have to take your own measurements.

AC_Hacker · 02-08-14, 11:12 AM

Quote:

Originally Posted by MN Renovator

Of course passivhaus ignores the temperature that an area reaches.

MN Renovator,

I am curious if there is an alternate universe where this is true?

Your quote either has a massive grammatical error, or else the principles of Passive House design are not well understood.

The primary Passive House design tool (Passive House Planning Package or "PHPP") has detailed historical data of local weather conditions worldwide, and it absolutely does take into consideration local weather conditions.

I think that a good place to start would be Wikipedia's Passive House entry.

It also has a lot of links that can help you to further your understanding.

As I said, it is a very sophisticated and well-developed approach to super high efficiency house design and construction.

-AC

MN Renovator · 02-08-14, 11:50 AM

What I'm saying is that the passivhaus standard requires you to insulate the house to an insane level if you are at the arctic circle. For example If you are in Portland, OR or a coastal California area where it doesn't get colder than freezing very often, you can get away with much less. ..of course temperature matters to get to the goal heat load.

davisk · 02-09-14, 02:03 PM

The heat strip in the plenum is code in my area and in my opinion the best way to go.
It should be sized to heat your whole house should the GSHP does not run. If loop size (excavation costs) are not a factor to you, over sizing a little would not hurt. Living in Canada I have my system sized at approx. 120% of maximum heat demand. It may have cost about $1000 more at construction but I have never had to use additional heating.

MN Renovator · 02-09-14, 07:12 PM

Quote:

Originally Posted by AC_Hacker

But 4.75 kBtu/sf/yr is the definition of the passive house. A Passive House that can meet the standard in Southern California would obviously not work in Indiana, it would need to be built different to achieve 4.75 kBtu/sf/yr.

It is a very stringent standard.

A house that can meet 4.75 kBtu/sf/yr does not require a heating system.

It's a revolutionary concept.

It takes a while to wrap your head around it.

-AC

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.

AC_Hacker · 02-09-14, 09:57 PM

Quote:

Originally Posted by MN Renovator

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

Stop right there...

The Passive House standard is 4746 btu/ft² per year. (taken from the Wikipedia entry)

Now... look at these two standards

4,750BTUhr/sf/year
4746 btu/ft² per year

What difference do you see? (I'm not talking about the difference between 4750 and 4746... it is of little consequence)

Can you see any difference???

-AC

MN Renovator · 02-09-14, 10:35 PM

It's 15kWh per square meter per year, rounded or not the difference between 4746 and 4750 is extremely small. 4746 is 99.915% of 4750. The difference is small and for what it is worth, you simplified it yourself on post 42 of this thread.

So subtract 8400 from 9,975,000 and subtract about 2.5kWh from 2924kWh if you factor the resistive heating figure.

You're splitting hairs. My roommate burned through more than 12kWh today, maybe I need to tell them that 2.5kWh over a year is something to fret about and maybe they will change their wasteful ways. Unfortunately my roommate is stupid so that doesn't work.

Edit: nevermind, I see I put btuhr when I meant btu. ..but the rest of the math was accurate for the 4750 figure versus 4746. You multiply it by the square footage.

02-09-14, 10:35 PM	#50
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	It's 15kWh per square meter per year, rounded or not the difference between 4746 and 4750 is extremely small. 4746 is 99.915% of 4750. The difference is small and for what it is worth, you simplified it yourself on post 42 of this thread. So subtract 8400 from 9,975,000 and subtract about 2.5kWh from 2924kWh if you factor the resistive heating figure. You're splitting hairs. My roommate burned through more than 12kWh today, maybe I need to tell them that 2.5kWh over a year is something to fret about and maybe they will change their wasteful ways. Unfortunately my roommate is stupid so that doesn't work. Edit: nevermind, I see I put btuhr when I meant btu. ..but the rest of the math was accurate for the 4750 figure versus 4746. You multiply it by the square footage. Last edited by MN Renovator; 02-09-14 at 10:47 PM..

02-07-14, 11:47 PM	#41
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	The Passivhaus standard is a bit strange but keep in mind that the passivhaus standard has an OR in there. "The specific heat load for the heating source at design temperature is recommended, but not required, to be less than 10 W/m² (3.17 btu/h.ft² per hour)." This allows my heat load of my 2100 sq ft house to be 6657BTUhr(my design temp is -11f or -13f depending on where I look). Now in his 1000 sq ft bungalow that would be 3170 BTUhr at design temp. A question that I've never seen the answer to is how the design load in Germany is derived. In the US, design temp is the point where it warmer than that temp 99% of the time(or colder 1% of the time depending on how you look at it). 1% of a 8760 hour year is 87.6 hours. What standard does Germany use, is it ASHRAE? Either way, I'm sure the design temps aren't far off but that's just an aside. For my house, to get to 6657BTUhr at design temp, I need the absolute best U-value .11 windows(R9), R100 in the ceiling, R45 walls, and to not lose much through the basement. Of course passivhaus ignores the temperature that an area reaches. If my design temp was 15 degrees, I'd be okay with R35 walls, R60 ceilings, and a much more affordable U-value .2 windows (R5). Instead of going passivhaus, I'm willing to use those numbers to get to just under 10k design load. 4 inches of rigid foam makes life easier and I'm content with a heating bill consisting of about $40 of natural gas or cutting the $210 of natural gas connection fees and moving things to mini-split electric. Sure my winter months will cost more but there will be a good savings by not paying the connection fee. Now with a GSHP, taking a look at an example manufacturer, how about the biggest one Waterfurnace. Their smallest unit isn't even offered with an ECM motor so the efficiency is a bit lower but with the low load I think it is good enough. Fans law indicates to us that lower air flow is less power needed. Their 5 series model 012 unit at 4gpm flow and 400 CFM airflow provides 14,500BTUhr cooling at 59 degrees entering water temp with 25.5EER and 12,300 heating with 50 degree entering water temp and 4.5 COP. If you've got an R30 wall, R80 attic, etc. 1000 sq ft bungalow that needs more than 12,300BTUhr heating, you need to work on the infiltration losses.

02-08-14, 10:52 AM	#44
jeff5may Supreme EcoRenovator Join Date: Jan 2010 Location: elizabethtown, ky, USA Posts: 2,431 Thanks: 431 Thanked 619 Times in 517 Posts	I tried a demo of the Technisolve software for a few days before i knew about coolpack. It is kind of like the autodesk/autocad software scheme: they have a plethora of modules that are each built for a specific purpose. If you are designing boilers, they have a different module that works well for that. If you are doing a heat pump, they have a condenser designer module that does the same basic thing. The thing I liked best about it was the wide variety of refrigerants in the database to select from. Coolpack, otoh, is very compact and generic in nature. To me, it is easier to use, since you don't have to learn five or six modules of software to put together a simulation. Once you learn two or three modules, that's about it. However, you usually have to look up your own data for accurate representation of components. Luckily, the mfr's post up thorough data on their products at ASHRAE conditions on their spec pages. Sometimes you have to take your own measurements.

02-08-14, 11:50 AM	#46
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	What I'm saying is that the passivhaus standard requires you to insulate the house to an insane level if you are at the arctic circle. For example If you are in Portland, OR or a coastal California area where it doesn't get colder than freezing very often, you can get away with much less. ..of course temperature matters to get to the goal heat load.

02-09-14, 02:03 PM	#47
davisk Lurking Renovator Join Date: Feb 2014 Location: B.C. Posts: 1 Thanks: 0 Thanked 0 Times in 0 Posts	The heat strip in the plenum is code in my area and in my opinion the best way to go. It should be sized to heat your whole house should the GSHP does not run. If loop size (excavation costs) are not a factor to you, over sizing a little would not hurt. Living in Canada I have my system sized at approx. 120% of maximum heat demand. It may have cost about $1000 more at construction but I have never had to use additional heating.