Remodeling the office (new floor, ceiling & adding insulation) passive house retrofit

[Daox]

Originally Posted by AC_Hacker

Daox,

I don't know if you have done hydronic heating before, or if you have gone through the steps to size and select the proper pump...

Thanks for the links.

I was looking at even the first formula and wondering how you can estimate your temperature drop accurately? I know how much heat I need to put out per hour and what fluid I'll be using. Its just the temperature drop that has me wondering.

[AC_Hacker]

Originally Posted by Daox

Its just the temperature drop that has me wondering.

To keep things in perspective, you're only doing one room, so the total cost to you in the long run between a pretty good design and a very efficient design will be small. Also, I don't know to what extent you have considered combining your solar project with your radiant floor, because there is a difference between radiant floor for fossil fuel and radiant floor for low temperature heating.

Regarding temperature drop, I think you'll find the hydronics programs to be a good tool in that regard. As I said before, I found RadiantWorks to be very useful (Taco has one too). It will do a heat loss calc and calculate how much hydronic heating will be required to offset the heat loss. It will even calculate the impact of layout.

But the issue I'm trying to point out is that you can affect the size of circulator pump that you'll need by the layout design. It all has to do with fluid friction and the more fluid friction you have (AKA: head loss), the larger pump you'll require, thus the greater power requirement.

The factors that will raise fluid friction (head loss) are:

• viscosity of fluid
• diameter of tubing
• length of tubing
• type and number of brass fittings you use
• velocity of fluid through the tube

To reduce fluid friction:

• Use larger diameter tube
• Use shorter runs
• Use parallel runs
• Use fewer fittings
• Use lower fluid velocity

So you will need a certain minimum temperature of water, flowing at a certain minimum rate, through tubing spaced at a certain minimum distance in order to achieve your desired heating level.

It's really a balancing act to get the heat you need and to minimize the power required to do it.

From the literature I'm going through, I 'm finding that too many professional installers over-specify everything in order to not suffer a call-back... and the home owner foots the bill in excessive energy costs.

In the days of cheap fossil fuel energy, if the radiant floor didn't produce enough heat, you could just turn up the boiler a few degrees.

But if you're trying to go solar, or in my case geothermal, you have entered the world of low-temperature heating. If the radiant floor isn't producing enough heat, how do you turn up the sun a few degrees or turn up the earth?

I guess what I'm saying here is that low temperature heating has extra demands that a DIY guy needs to be aware of.

To conclude, low temperature heating really is on the bleeding edge, it shouldn't be, but it is. I have been in touch with John Siegenthaler, and he is every bit the phenomenally informed guy we would hope he would be, but he hasn't yet really stepped over the line into low temperature and very low temperature (yes, there is such a thing) heating. And also the computer programs I have tried don't go very far into it either. However, I have found that RetScreen has been used in this context. RetScreen has a very steep learning curve, but it's power is that it is very flexible.

-AC_Hacker

[Daox]

I have John's latest book on hydronic heating. However, I haven't finished reading it. I'm only about 1/4 - 1/3rd the way through it I think. Lots of reading yet to do!

I really want to rely on the solar as much as possible. It may never provide 100% of my heating load, but the higher the better. Therefore I'm very interested in low temperature hydronic heating. The boiler will be a backup heater although I'm sure it'll be used a lot more than I'd like.

[AC_Hacker]

Originally Posted by Daox

I have John's latest book on hydronic heating. However, I haven't finished reading it. I'm only about 1/4 - 1/3rd the way through it I think. Lots of reading yet to do!

I really want to rely on the solar as much as possible. It may never provide 100% of my heating load, but the higher the better. Therefore I'm very interested in low temperature hydronic heating. The boiler will be a backup heater although I'm sure it'll be used a lot more than I'd like.

Daox,

I thought you'd be interested... here is an article Siegenthaler did regarding hydronics in low-load houses. I think it has relevance to what you're doing. My quibble is that it doesn't really tackle low-temperature heating head on, discussing how to maximize the low-temperature potential of radiant floor heating.

-AC_Hacker

[Arkaneinc]

I have to redo my office at my house so am curious to see how the flooring looks when finished

[gasstingy]

If you are reporting your income on the room as you are required to do, listing the expenses and taking credit for them is allowed in our tax code. Some items {depending on the amounts} can be expensed in full, others {longer-term improvements} would have to be capitalized and depreciated.

Give your accountant the information at the end of the fiscal year and let him/her work it up. They do that all the time. It's a relatively simple task for a person with enough knowledge to file a return on a non-profit {or even a for profit} business.

[Daox]

This project is progressing again. I just ordered windows for the room. The door to the outside will be remove and replaced with a window and I'll be adding another window next to that one. The reason for adding windows is the room is relatively dark being in the middle of the house.

With this being my trail room before I start renovating the upstairs, I wanted to try out the best. In this case I found the best to be Serious Windows 925 series. They are pricy but also have an r-value of 6.3 (high solar heat gain model). These are the windows that people are using in passive houses. While I highly doubt that I'll ever achieve a passive house certification, the goal is to get as near as possible to it.

I have also figured out what I'l be doing with the outside wall for insulation. I will be using a single layer of rigid foam board with expanding foam around it like AC Hacker has done in his house. This is by far the easiest and cheapest way I've seen to seal up the house an insulate at the same time. Beyond the rigid foam I will be extending/thickening the wall on the inside with a larsen type truss. That cavity will be filled with cellulose. I think I will aim for R40 walls. If I ever outsilate, that will leave me room to bump up the r-value, and I won't loose much inside area.

[S-F]

Good luck with those Serious windows. I'd go that route if I had the $. Well, maybe I would. I'm glad to see progress on this. I'd been thinking you had finished it and not updated the thread. I look forward to seeing more pictures.

One thing though. You can't outsulate with foam if you've already insulated with it. You can't make a vapor barrier sandwich. Your sheathing and structural lumber will rot. A wall has to be able to dry to AT LEAST one direction.

[Daox]

I am planning on putting 1-2" of rigid foam between the studs, not cover/seal them completely. The cellulose will be covering the rest of everything. Is that not enough? Would dense pack cellulose even allow wood to dry behind it? I've heard it doesn't let air through hardly at all.

I'm not sure if I'll continue using the 925 series Serious Windows upstairs, or if I'll just downgrade to a lower series model. It really just depends how much I like these windows and how they perform this coming winter.

[S-F]

I think your current plan is sound. In fact, I think I suggested it at the beginning of this thread. But at any rate, it will be fine as long as you don't put foam on the outside of the sheathing. then your sheathing would be sandwiched between vapor impermeable materials. If you don't do that then the sheathing can dry to the outside. Personally I think that if foam must be used it should be on the outside to keep the sheathing warm. There have been numerous studies showing how warm sheathing is good sheathing. But if you do that then you can only put so much cellulose on the inside because the majority (60% at least) of the R value needs to be in the foam to prevent the dew point from happening inside the cellulose. So if you outsulate with foam on a 2x4 wall you can get R 13 in cellulose and R 30 something on the outside in foam. This 60% foam, dew point stuff is something you should also keep in mind when you decide on how much foam to put in there. Cellulose is very hygroscopic and national Fiber says that theirs can cope with 30% of its weight in water before failure, but you could reach 30% pretty fast in a moist environment with the dew point in the middle of a wall with limited drying capabilities, i.e. a vapor barrier on one side. Many of the builders I know are going so far as to use CDX instead of OSB, even though it's more expensive, because it's more vapor permeable. As always, a rain screen is recommended. Go with a rain screen and don't have the need to paint your house again for 20 years. Let's take Robert Riversong for example here. He's been making walls with no vapor impermeable materials aside from interior paint for decades. Not even any sheathing. Sounds crazy to me but his houses are working, and working quite well. I honestly think he's got the right idea but air tight drywall sucks. You can't add an outlet in an exterior wall later down the line.