Posted By FBBP on 18 Feb 2011 12:50 AM

Posted By pura vida on 18 Feb 2011 12:30 AM
so even though not really icf related, as stated above, i'm leaning towards doing an icf basement and a double wall for the main floor and garage. 1 to 2" of eps on the outside, 2X4s for the outside wall 2X3 inside walls. is it possible to put the vapor barrier on the outside of the inside wall to avoid electrical and plumbing breaks? the point being able to maintain a more constant vapor barrier throughout the house. would this help with the mold issue? or am i missing something? what about putting the foam on the inside wall?

pv

pv - it is certainly possible and will give you a better v. b. but you should reread Dana's comments on the moisture situation. Depending on how you install the eps and what "filler" you use in the space, you might be better off with no v.b. Dana has given some pretty in depth discuss about dew point and breathablity of walls

thanks, i'll do that.  have been busy lately and haven't had a chance to really dig into some of the more in depth info.

that cost estimate did not include any floors.  just foundation and walls.  although i will probably do some sort of slab on grade and then add the icf.  maybe...

Well, I'm going to toss out a couple of things for interest sake. First, here's what 4 different HVAC programs kicked out for heating load for my 2000 sf ICF house, w/ ~ R40 spray foam on the roof deck. I use the crawl space for the supply plenum and the attic for return.

Wrightsoft - 33341 Btuh
HVAC Calc - 33241 Btuh
HEED (Manual J output option)- 35761 Btuh
HVAC Sizer for Concrete Homes - 19000 Btuh

 I'm heating with a 3 ton Daikin VRV-S air-to-air heat pump. The factory performance chart shows an output of 28300 Btuh and a power input of 3.13 kw (10692 Btuh) for a COP about 2.65 at an outdoor temp of 9°F and an indoor temp of 75F. This is close to the conditions of this past Jan 3 & 4 here in SW Idaho. The two nights were around 9 and 10F and we keep our house at 74F. 9F is the Manual J design temp for this area. The heat pump has no auxiliary heat strips. As I recall the house temp may have dropped 1° by morning those two days.

Below is a copy of our hourly power use as shown on our account info at Idaho Power. We have smart meters now. You'll see that during the night our total power consumption is around 6 kWh per hour. This would be the time of maximum heat load. From 1 PM to about 7 PM the load is lowest indicating there is very little heat load. I believe the swing you see on the chart is a combination of the daily power use for living activities such as cooking, hot water, TV, computer, etc. plus the heat load variation between afternoon/evening and night/morning. The peak loads are probably cooking times, or oven cleaning, and water heater, maybe even dishwasher. I'm sure the peak on the night of the 4th is the water heater. I have two, one with heat pump and one regular electric in the garage. The garage temp dropped to around 48F on the coldest nights so I'm attributing the peak to the water heater kicking in to make up for jacket heat loss to the garage.

If we subtract the heat pump 3.13 kw from the total load of 6 kw and convert that to Btuh, and then multiply by .9 we have about 8800 Btuh. This is an approximation of the heat derived from the electricity that is used in the TV, computer, light bulbs, etc. Nearly all the electricity that comes into the living space eventually degrades to heat. In my case the water heaters are in the unheated garage and I have outdoor lights. The 8800 number is somewhat of a swag, but even if it's off by 50% the end result doesn't change a whole lot.

Adding 28300 to 8800 we get 371000 Btuh total heat input into the house for the coldest hours of the night on Jan 3 & 4. That is pretty close to the calculated heat load for three of the programs. I really wonder about the HVAC Sizer number as it is low by almost 50%.

Based on my experience with two winters of heating I would argue that the latest version of Wrightsoft will provide a reliable number for heat load calculations for an ICF house.

Sorry about the quality of the image. Apparently Idaho Power wants to discourage copying the charts as they have gray numbers on gray background and I combined two days graphs into one.

dmaceld - this is very interesting! Thanks so much for taking the time to put this together for us! As you know these do not match what I have for my house so of course I am most interested to see what we can compare. I need to give this some more thought, but two observations. One - I agree with you that most of the power consumption in a house turns to heat. Does any of this happen from 10 pm to 6 am (other than the hot water heater)? Around here, unless I'm up and on the computer like tonight, the only power loads that would be on are fridge/freezer and phantom loads. Based on that would it be fair to suggest that almost all the early morning power is going to the heat pump? Two - Mr Wright is listed as one of the consultants/authors of the concrete sizer.

4 to 8 AM, sometimes longer, I have a 500 watt load that is heat pads in the shower walls and floor. Other than that, a small night light and phantom loads like on the stereo and TV and a 120v/240v transformer on each side of my UPS for the computer. The UPS was a bargain internet purchase over 10 years ago and is a 240v unit. Then of course refrigerator and freezer. The air handler for the heat pump system runs constantly but it's rated less than 500 watts for the fan motor, and I've got an ERV that runs 20 mins every 2 hrs. I'm still working on trying to figure out where all the power is going, but the minimum power draw is about 2 kw per hr based on power bill for April and October when neither heat nor AC runs hardly at all. I've got a couple of Kill-A-Watt meters I'm using to get a handle on things. I'm thinking my computer set up may be a bigger power hog than I've thought.

I've no idea if the Wright you say is associated with HVAC Sizer has any connection to Wrightsoft. Actually I think it's called Wright Suite. It's the premier heating and cooling s/w program for contractors, and costs several thousand dollars. It does duct sizing and I don't know what all. Your fly-by-dusk AC contractor is not likely to have it or use it, and may not even know it exists. Considering the size and value of Wright Suite I would doubt the author would involve himself in a $60 competitive program, but I could be wrong.

I just looked at a couple more charts at Idaho Power. On a Sunday afternoon when we aren't home the min power draw drops to 1 to 2 kwh/hr.

dmaceld, very interesting and thanks for sharing!

Here are a couple of questions followed by suggestion of a couple of small experiments.

How id you determine that 20 mins every 2 hours was required for your ERV? I run mine 20 minutes once a day (and whenever someone deliberately turns on a bathroom fan it runs for 20 minutes). 4 hours a day or so seems like a huge amount of time to me -- wouldn't this cause your Daikin to kick on over and over again? You have an ERV and not an HRV, correct?

I had an energy expert try to talk me out of installing mine at all -- he said i was hardly Howard Hughes. I installed it anyway after some research but run mine far less often.

What is the consumption of your ERV?

I had a house here a few years ago that was using a very cheap ERV (basically it was a fan) and it was running all the time and causing the AC to short cycle over and over again.

Anyway, since you have the smart meter -- it would be interesting to turn your ERV off for a night or two or run it only during the daytime and see if you get some interesting data.

Regards.

dmaceld - I thought I had read that it was the Wright however I can not find that back so I will definitely retract point Two. My apologies. I am familiar with the Wrightsoft software. The gentleman who did my calc's had just come back from a training course on it and it is my understanding that that is the only software they use. If we take the remaining 4 kws as heat load @ COP I think you are using slightly more than your worst case scenario but way more than the concrete calc. What is the run time of your heat pump? Is it running close to full out at the design day i.e. Jan 3 & 4? I'm a little surprised at the lack of longer lag time from the heat soak of the day. I would have hoped for the heating ramp to be much shallower and not peak till 3 or 4 in the morning but I guess some of that is the difference between hot water in slab and forced air. The ERV is a bit of an unknown. I am not using any at this point as we are not living in the house. It does not really belong in the actual building heat loss calc's as it is user defined but at the end we still have to heat that air so it is definitely part of the whole equation. I hate sick houses so I will probably run my fresh air source in a similair pattern to what you are. I'll bet those 2 kilowatts bug you a lot the more you thing about it ;-) Sorry for the long running paragraph, GBT doesn't recognize the return strokes I put in (must be a Mac thing)

Posted By TexasICF on 19 Feb 2011 08:57 AM
How id you determine that 20 mins every 2 hours was required for your ERV? I run mine 20 minutes once a day (and whenever someone deliberately turns on a bathroom fan it runs for 20 minutes). 4 hours a day or so seems like a huge amount of time to me -- wouldn't this cause your Daikin to kick on over and over again? You have an ERV and not an HRV, correct?

I had an energy expert try to talk me out of installing mine at all -- he said i was hardly Howard Hughes. I installed it anyway after some research but run mine far less often.

What is the consumption of your ERV? 

The 20 min/2 hr run time is the minimum available with the optional control unit. I have an Ultimate Air unit. The controller has a fixed two hour cycle time with 4 run time options - off, 20, 40, and 60 minutes. It does not override the speed setting on the main controller and I have it set it at near the minimum fan speed. I just took the Kill-A-Watt meter off it. It shows 787 hours elapsed time and 12.63 Kwhr used. That's less than 0.4 kwhr/day, well within the noise of all my data. That works out be about 138 Kwhr/yr for an annual cost of $10. The humidistat in the bathroom kicks it in at high speed for maybe 10 minutes most mornings. I seldom need to turn it on for deodorizing purposes as we have constant air circulation in the house.

I selected an ERV because that's all Ultimate Air makes, and their unit is the only one I found that offered an Economizer mode of operation. The run time will go up considerably in the summer. I have the economizer option connected to a second thermostat with 2 stage cooling. The first stage stops the heat exhanger in the ERV. The second one puts the fan into full speed mode. So, when the outdoor temp is below about 70F, and the indoor temp goes above AC setting, the ERV simply exchanges cool outdoor air for warm indoor air. I have another thermostat in the incoming air so if the outdoor air is above about 70F the Economizer mode is disabled. The only downside using it for cooling is the volume of air is nowhere near what I wish it were. The max air flow through the Ultimate Air 200DX is ~200 CFM. I'd like to have about 2000 CFM!

I'll probably plug it into the Kill-A-Watt in the summer to see how much the Kwhr goes up.

Posted By FBBP on 19 Feb 2011 10:21 AM
If we take the remaining 4 kws as heat load @ COP I think you are using slightly more than your worst case scenario but way more than the concrete calc. What is the run time of your heat pump? Is it running close to full out at the design day i.e. Jan 3 & 4? I'm a little surprised at the lack of longer lag time from the heat soak of the day. I would have hoped for the heating ramp to be much shallower and not peak till 3 or 4 in the morning but I guess some of that is the difference between hot water in slab and forced air. The ERV is a bit of an unknown. I am not using any at this point as we are not living in the house. It does not really belong in the actual building heat loss calc's as it is user defined but at the end we still have to heat that air so it is definitely part of the whole equation. I hate sick houses so I will probably run my fresh air source in a similair pattern to what you are. I'll bet those 2 kilowatts bug you a lot the more you thing about it ;-)

Not sure what you're driving at with the 4 kw at COP. The heat pump has a variable speed compressor so at those cold temps I'm sure it's running pretty much at full speed and the power consumption is at the max for those conditions. So all power above the 3.13 kw pretty much has to be all the other loads in the house. The COP for all those can't be above 1, the same as straight electric resistance heat, except for what is consumed in the heat pump of the one water heater. That's why I'm adding about 8800 Btuh to the 28300 Btuh from the heat pump for the total of 37100. The COP of the heat pump is about 2.65 at the cold temps according to Daikin.

The lag time is not as long as I thought it would be either. Generally speaking, the heat pump turns on in the evening some time, maybe even as late as 9 PM. It usually then runs continuously until late morning. But since it is variable speed, even though it's running, it's running slow. This is much the same in the summer for cooling also. Most of the time it cycles on and off once a day.

Air changes are part of the usual heating/cooling load calculation. It's not an add-on, but you do input the value into the program. It's surprising how much of an impact air changes can have on total heat and cool load. That's why installing an HRV or ERV is should be considered.

The water heaters are very definitely a factor in the total load. My latest data indicates the two water heaters are consuming about 6200 kwhr/year, or about 17 kwhr/day. The straight electric heater runs about 8% of the time, or about 2 hrs/day. It's easy to see how it can add a 4.5 kwhr/hr load to the other loads and cause the peaks, since it's not variable. It's either on or off.

For comparison here's the chart for Feb 1. That was one of the peak hour days. The min temp for that day was about 20F 4 to 9 AM and about 10 to midnight. This one shows the lag pretty clearly.



I was going to get some more data from Idaho Power and make some more comparisons, but the accounts section of their web site is down for maintenance.

dmaceld - what I was get at was based on the you indicated that your base load was 2 kilowatt (shoulder season) the rest is heat. (at night there would not be any additional lights etc. so the values for all the rest should be similair to the shoulder season.) Of course the air changes have to be calculated for heat load. I was just thinking that to compare ICF to stacked up stick or to try to determine the effective R value for ICF we would try to eliminate as many variables as possible. How many air exchanges we want is not the fault of the building envelope. It would be interesting to see what your values in the different softwares are without the air exchange. How does one go about checking to see it a unit is actually performing up to manufacture's spec's?

FB, As I remember I used pretty much the minimum choice for air changes in the programs, which I think is .35 ACH. Looking at my comparison s/s three programs calculated about 1/4 of the total heat load being the air change heat load. WS is about 8500 Btuh out a total of 33300 Btuh. HVAC-Calc and HEED are close to the same. HVAC Sizer didn't break it out separately in the final number. For HVAC Sizer I used the minimum built into the program, 0.02 cfm/sq ft, which would be about .15 ACH. It has a graph that indicates about 12% of the heat load is due to infiltration.

One thing I did not do with any of the programs which had a provision for it, was add in heat generated by in-house equipment such as fridge, stove, TV, etc. That's why I'm taking almost all of the power as heat input into the house, with no more than the rated max draw of the HP at COP. The more well insulated the house is, the greater the proportional value of the heat from daily living. That complicates proper sizing of the heating and cooling system. It reduces the required furnace or HP size for heating, and increases it for AC sizing.

The only part of HVAC equipment performance ratings that can be easily verified after installation is the power consumption. With hydronic you can put in a flow meter in the piping, and measure the temp difference and calculate the heat put into the house. But with air system it really get problematic to get reliable data. I'm really not ready to shell out the bucks for a power meter system to measure the power into my HP. That's why I'm relying on the mfr tables. But I do wonder if there is a discrepency between what's real and what's on paper.

Another complicating factor with the HP performance, and which I have ignored, is the defrost cycle. I do know the HP coils do frost up pretty heavy in the really cold weather. That undoubtedly is a significant portion of the power consumption of the HP and does not contribute on an instantaneous basis to the heat input into the house. That is a shortcoming in my attempt to estimate the house heat load for a given one hour time span.

Actually, my heat pump, although marginal at best according to calculations for the coldest hours of the night, does a great job of keeping the house warm. I really expected to have to use the pellet stove for auxiliary heat on the really cold days but that has not been the case. How much of this can be attributed to the HP performing better than expected and how much is because of the non-HP power load being greater than anticipated and being converted to heat, I don't know.

I think one big reason we don't see the heat cycle lags we would expect to see is because of thermostat sensitivity. The HP kicks in when the house temp drops no more than 1 degree below set point. The controller keeps the HP from raising the house temp more than about a 1/2° above set point, and doesn't let it drop below about 1/2° below set point. The Daikin HP has a pretty sophisticated control system for a home heating system!