Thoughts on Comfort Plus or Low-e type glazing « Alternative Technology Assn Forums

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Thoughts on Comfort Plus or Low-e type glazing

(25 posts) (15 voices)

Started 11 years ago by bundy
Latest reply from dlvb19

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bundy
Member

Hi there, I have had conflicting info on Low-e or Comfort Plus type glazing options. One Solar Architect who I do respect says that Normal 4mm glass has an R value of about 0.15 whilst this Low E glass has an R value of about 0.32 but costs significantly more (In our case approx 70% more than 6.83mm Laminiated glass) and he says it is not worth that extra cost. In his opinion Heavy drapes and pelmets work far better.

In our situation that setup is not possible so I am looking as to what else I can do. We are planning large floor to ceiling Bifold doors around our main living area opening on to a rear verandah. Frame construction will all be from Timber so heat transfer via the aliminium frame is not an issue.

The Viridian or Pilkingtons Sales reps rave about the glass being 100% better than standard glass, which I guess it is but is the increase enough to make any useful and cost effective difference?

I am more concerned with Heat loss in winter than heat gain as we have good shading where needed.

I am just not sure if it is worth the added expense of putting in this type of Glass and would be very interested to hear from anyone who has used it and what they think of the result

Was it worth it or would I be better of spending the money in other areas like more Solar panels etc?

Posted Wednesday 27 Oct 2010 @ 12:43:57 pm from IP #
dave lawrence
Member

what climate zone are you in ?
double glazing would be superior .
your solar architects advice was spot on .
look at http://www.yourhome.gov.au/technical/fs410.html

Posted Wednesday 27 Oct 2010 @ 7:12:13 pm from IP #
termite
Member

I'm of limited assistance here, because I have not actually been inside yet but...
I had a wall of fixed windows/louvres/sliding doors installed with 6mm 'comfort plus' glass around June this year (the house is mine, but currently rented as I'm working interstate). Location: coastal Sydney. The glazing forms the entire south wall of a living area with a raked ceiling, which also has 2/3 of the eastern wall in double glazing (DG). Measurements - about 5.4m wide, from 2.1m high at one side to 3.6m at the other. Years ago, when I put in the DG, I didn't notice any particular thermal barrier improvement, but the south wall was still plain glass, and probably leaked heat like a sieve.
The chippy reported a noticeable improvement in the warmth inside with the new glass. That's it - no thermometer readings, just it felt better. It is a difficult surface to cover with blinds or curtains, due to the triangular shape of the top, and I didn't want permanently closed blinds - you get a good view of storms coming up from the south.
As for cost, well I did not get a comparable quote for plain glass. But it cost $15k.

Posted Wednesday 27 Oct 2010 @ 7:30:00 pm from IP #
bundy
Member

Thanks Termite, Sounds similiar to us as in that we are wanting to keep these windows / doors uncovered by Curtains also for the view and astheitcs nothing else, from what you say your "Gut feel" is it seems to work. Which is as good a guide as any.

Dave FYI we are located in Perth, WA.

Posted Thursday 28 Oct 2010 @ 5:33:32 am from IP #
arnaveed
Member

I want to make sure I understand where exactly you want to mount the shutters. Do you want them mounted on to the sliding doors themselves or so that they overlap the entire opening of sliding doors?
Also, will the shutters be a fixed louver or operable louver?
Most of the sliding door hardware by Johnson Hardware does not require a bottom track. Instead they use a small guide placed on the floor only where the shutters or doors would overlap when closed.
If you can answer my questions above I will be able to give you more specific help.

Posted Saturday 30 Oct 2010 @ 8:28:42 am from IP #
termite
Member

Spam alert?

Posted Saturday 30 Oct 2010 @ 9:46:15 am from IP #
termite
Member

Re shading windows with a triangular top (interior blinds):
I know external shading is much more effective, but just sometimes it's a bit difficult and expensive to get it windproof, weatherproof (durable) and retractable.

I just saw a window shade on Grand Designs series 4 - it retracts in two stages, the lower part is a standard duette-style blind. Once that is fully retracted, the remaining triangle of blind then retracts like shutting a Japanese fan.
Annoyingly, this is not available from any suppliers that I can find in Australia. Perhaps I can trace the product from the UK.

Posted Tuesday 4 Jan 2011 @ 3:55:50 am from IP #
TonyT
Member

For R=0.15 the heat conducted through the glass is U=1/R =6.67Watts/square metre of glass per degree C.
For R=0.32 U=3.125W/sqm/degC
The Heat loss when Comfort Plus is used is reduced by (6.67-3.12)=3.5W/sqm/degC
If the temperature inside the room is 15degC higher than the outside temperature the heat loss is reduced by 3.5*15 = 52.5W/sqm.
Over 24hrs the reduction in heat loss is 52.5*24 = 1260Watthours/sqm or 1.26kWhrs/sqm.
If the room is heated using an electric-resistance heater with electricity costing 20cent/kWhr this reduction in heat loss is a saving of (1.26*20)=25cents/sqm per day.
A heat pump delivers about 3 kWhr of heat from one kWhr of electricity.
If the room is heated using a reverse cycle air conditioner the electricity saving is about 1/3 or 8cents/sqm per day.

Posted Tuesday 4 Jan 2011 @ 5:42:40 am from IP #
cool at home
Member

TonyT's data is pretty convincing, I would think... over the lifetime of the windows.

I have Comfortplus throughout our house and can't say for sure how it 'feels', but it is pretty easy to keep warm/cool (we think... we've only lived in this house with this glass, and there are many variables between houses to consider). From our perspective it was too 'risky' to stuff up all we've done with materials, aspect and insulation by putting in lots of 'ordinary' windows. Pretty much undermines all the other expenses, because windows are a key source of heat gain/loss.

We recently installed a new (Comfortplus glazed) triple panel glass door in our family room, very wall shaded and on northern aspect, and (as proof that ANY windows transfer heat far more than well insulated walls) have been shocked at how much warmer the room gets.

But we haven't put up the pelmet and 'triple pass' curtains yet, and I do swear by those... summer and winter! I definately agree that they are an easy, relatively inexpensive and very effective way to manage the temperature of your rooms (in addition to adjustable awnings to keep out summer sun).

I would seriously consider the 'no window coverings' plan - views will be great (during the day) but you WILL be creating an environment that gets far warmer/cooler than it would be with window coverings pulled to keep heat in or out at particular times during the day and night, and so a room that is far more costly to heat/cool.

I recently visited a large home with beautiful big, uncovered windows and a $3K per quarter electricity bill. I didn't even pay that much for all my curtains... and my bill is around $300 per quarter. At least 4 days a year I'm very, very happy to have curtains. And when I really want them pulled back, they are.

Posted Wednesday 5 Jan 2011 @ 6:07:44 am from IP #
munter
Member

I agree that Tony's calcs are useful in understanding the heat loss perspective but, depending on whether the windows in question will receive winter sun, the heat gain side should also be considered.

Low-E glass has a lower Solar Heat Gain Coefficient, meaning that it permits less winter warmth from the sun's radiation through. If you are relying on these windows to let winter sun in for warmth then Low-E windows will warm the house less during daylight hours. In this instance I think double glazing with plain glass (which has a higher solar heat gain coefficient and and even better U-value than Low-E) might be an even better option.

Posted Monday 10 Jan 2011 @ 12:11:25 pm from IP #
TonyT
Member

Viridian and other glass manufacturers all provide tables with R and U values for glass that is un-coated, coated, double glazed etc.
Many different coatings are available.
In winter, to minimise heat loss from a room while also maximising solar heat gain, the window needs a high resistance to outward heat flow plus a low resistance to inward heat flow.
Comfort Plus has a high resistance to outward heat flow but also a high resistance to inward heat flow.It also blocks most of the incoming ultra-violet.
All the required technical data is provided in the Viridian tables.
The key is to calculate the total heat loss kWhr (and the solar heat gain kWhr) and the value of that heat (at about 20 cent/kWhr) and compare the energy costs with the capital cost to buy the glass.
Note that using a reverse cycle air conditioner one kWhr of electricity produces about 3kWhr of heat so the cost of heat energy reduces e.g. to 20/3 = 7cent/kWhr.

Posted Tuesday 11 Jan 2011 @ 9:46:04 pm from IP #
TonyT
Member

Calculations made for the design of a new sun-room on the north of our cottage have surprised me.

The amount of heat that is lost through a glass window can be more than 20 times the heat that is lost through a well-designed and well-insulated wall.

With "smart" glass (or with double glazing), the window heat loss is still about 10 times the heat loss through a well-insulated wall.

For standard glass a typical thermal resistance "R" value is R= 0.15.

The thermal conductivity, U, is calculated as U=1/R.

As was shown in an earlier post, for standard glass U = 1/0.15 = 6.7watts per square metre per (degree Celsius of temperature difference across the glass).

For typical high E glass R=0.32 so U=3.13W/sqm/degC

For a timber frame wall constructed with gyprock inside, 100mm of fibreglass insulation, foil, a 50mm reflective airspace and weatherboard outside the total thermal resistance, R= 3.23 so U = 0.3 watt/sqm per degC which is less than 1/20 (5%) of the loss through standard glass.

During winter in the Adelaide Hills on a day without cloud the daily heat gain inwards through a North facing window with one square metre of standard glass is about 10 MegaJoules (or 10/3.6 = 3 kiloWatthours)per day.

For the same wall, the daily winter heat loss outwards through one square metre of low E glass is about 4MJ (or one kWhr per sqm per day).

For our room with a floor area of 40sqm, the optimum area of North facing glass works out to be 10sqm.

The glass will be selected to transmit all of the outside solar energy inwards but to minimise heat losses outwards from the room.

During summer the North and West windows will be completely shaded by removable eaves.
Honeycomb blinds will cover the windows when there is no view outside.

Posted Tuesday 12 Apr 2011 @ 11:37:22 pm from IP #
xanthe
Member

I love the scientific calcs and explanations so will leave this to the experts.
For a non scientific view (for what its worth)
We completed a 5 x 5.5 metre northerly extension to our house in Tasmania in April 2010. We used 6mm comfort plus glass in large wooden doorframes as a compromise to double glazing (this would have been my preferred option but I was firmly told by my husband and the builder that it could not be done with the sizing and use of wooden door frames). We installed a heat pump but do not need to have it on during the day in winter (just early morning first thing and in the evening).
We have found the room to be warm in winter and cool in summer and the comfort glass is a noticeable improvement on the ordinary glass.
So far we do not have any drapes - we enjoy the "orangerie effect" of the garden surrounding our living space, but no doubt we will eventually get something to assist with the retention of heat in the winter.

Posted Wednesday 13 Apr 2011 @ 4:10:53 am from IP #
TonyT
Member

There are many different types of "low e" or "smart" window glass.

In a hot climate, the goal is to exclude the heat from the sun during the day and to retain heat in the room when it is cold outside. "Comfort Plus" is the name given by one manufacturer to their glass that has been designed to deliver these and other useful properties.

In a cold climate, for an unshaded, North facing window, the goal is to transmit and capture the maximum heat from the sun during sunlight hours and also to retain heat inside the room. Manufacturers do make a type of glass that has these properties. It is not Comfort Plus.

The key is to obtain from the glass manufacturer the table that shows all of the properties of all of the different glasses and use the table to select the glass that performs to suit your needs.

An example table is at

http://www.viridianglass.com/products/downloads/Viridian%20Glass%20Performance%20Data%20-%20Energy.pdf

Posted Wednesday 13 Apr 2011 @ 6:41:10 am from IP #
schnark
Member

Hi All,

We're building our own house and needed to investigate the window properties as we were looking at ComfortPlus, standard Double Glazing as well as Low E glass. We had always planned to go Double Glazing but looked at ComfortPlus as were told its sometimes better in cold environments (in all cases bar SHGC, it turns out its not)

Here's the breakdown on the stats from one of our suppliers - figuired it might help others. These are for standard residential aluminium windows with air filling:

Sliding Window (ComfortPlus) - Cooling Stars (2), Cool% (35%), Heating Stars (3.5), Heat% (34%), SHGC (0.59)

Sliding Window (Double Glazing) - Cooling Stars (2), Cool% (37%), Heating Stars (4), Heat% (37%), SHGC (0.58)

Sliding Window (LowE) - Cooling Stars (2.5), Cool% (43%), Heating Stars (4.5), Heat% (42%), SHGC (0.54)

Awning Window (ComfortPlus) - Cooling Stars (2), Cool% (38%), Heating Stars (4.5), Heat% (48%), SHGC (0.53)

Awning Window (Double Glazing) - Cooling Stars (2.5), Cool% (40%), Heating Stars (5.5), Heat% (57%), SHGC (0.55)

Awning Window (LowE) - Cooling Stars (3), Cool% (45%), Heating Stars (6), Heat% (61%), SHGC (0.51)

Stacker Door (ComfortPlus) - Cooling Stars (2), Cool% (38%), Heating Stars (4), Heat% (38%), SHGC (0.59)

Stacker Door (Double Glazing) - Cooling Stars (2), Cool% (36%), Heating Stars (4.5), Heat% (42%), SHGC (0.61)

Stacker Door (LowE) - Cooling Stars (2.5), Cool% (42%), Heating Stars (4.5), Heat% (47%), SHGC (0.57)

Some general observations:
- Awning windows perform significantly better than sliding windows. They're also more expensive
- we live in Canberra so Heating is far more important than cooling - find out for yourselves what they key is for your area and then base your decision around that
- we plan to cater for summer heat gain through use of external awnings, decent curtains, eaves, decidious trees and a pateo. These are all incorporated into the house design
- we compared the above (standard residential grade) windows against the top of the line (magnum) option - the only improvement (bar the looks) was that the SHGC was slightly (generally 0.01) less (meaning you gain more sunlight), the cooling stars were on average 0.5 better for comfort plus (only). In general, it was sigificantly worst for heat%, especially for awning and sliding windows
- Push your suppliers for the WERS information, or at least the model numbers so that you can compare your options - you'll be suprised at the results - we certainly were

In the end, we're going with the LowE to maximise our heat retention. The price difference was as follows (note, these were trade prices so things may get marked up for retail):
- Comfort Plus = $X
- Double Glazing = 0.98 * $X
- LowE (with Double Glazing) = 1.09 * $X

Posted Sunday 17 Jul 2011 @ 6:46:54 am from IP #
schnark
Member

The other thing I neglected to mention was that when you compare the U values between the premium windows and the normal residential ones, the residential ones actually come out on top - i.e. they have a lower U rating. This again genuinly surprised us as we had been told the premium ones were much better....

Posted Sunday 17 Jul 2011 @ 7:33:23 am from IP #
dlvb19
Member

@ TonyT

I would love to see all your calculations relating to your 1/4 glazing/floor ratio, and any considerations like thermal mass, eaves .etc.

Posted Monday 18 Jul 2011 @ 9:58:53 am from IP #
TonyT
Member

dlvb19

The following post is copied from
http://www.ata.org.au/forums/topic/183

(quote)
Calculations for the planned 40 square metre room across the North of our cottage
indicate that if the temperature inside the room is 22degC and the temperature outside is 7degC (deltaT = 15degC), the daily heat loss during winter sunlight hours (from 7am to 6pm) will be 17kWhrs.

For our room, the calculated % of this heat that will be lost from each part of the room is:

28% Floor 40sqm @ 0.77W/sqm/deg
25% Windows 10sqm LowU+HiSHGC glass 4mm single pane in DIY wood frames @ 3.62W/sqm/deg
15% South internal wall (insulated-existing-wall+2windows+door) 31sqm
13% External Doors on East and West 25mm wood 3@2sqm
9% Ceiling 40sqm @ 0.32W/sqm/deg
9% External walls (North, East and West) 40sqm @ 0.31W/sqm/deg

After construction, if we need to reduce the heat loss we will add a second pane of standard glass (or perhaps try using tight, clear PVC film) spaced 12mm inside of each window.

From NASA at

http://eosweb.larc.nasa.gov/cgi-bin/sse/grid.cgi?email=tonyth2%40gmail.com&step=2&lat=-36&lon=138&num=319055&submit=Submit&p=grid_id&sitelev=&veg=17&hgt=+100

for the Adelaide Hills during winter, the average daily solar insolation onto one square metre of vertical window that faces true North is 3.8kWhr/day.

The glass tables at

http://www.viridianglass.com/products/downloads/Viridian%20Glass%20Performance%20Data%20-%20Energy.pdf

can be used to choose the type of glass.

Un-shaded "smart" window glass that has been chosen to retain heat within the room (low U value) and also to transmit the maximum of the solar insolation (high SHGC) will transmit about 70% of the incident solar insolation. With this glass, out of the winter daily available 3.8kWhr/sqm, 0.7 x 3.8 = 2.7kWhrs/sqm will be transmitted through the glass for room-heating during the sunlight hours.

The area of glass that is needed to replace the 17kWhr of heat lost from the room during winter sunlight hours is 17/2.7 = 6.2 square metres.

To capture some additional heat, we are planning to use 10 square metres of windows in this North facing wall.

My calculations suggest a rule of thumb: it may be that the optimum area of North facing glass for a room is about 25% of the floor area (i.e. 10sqm glass for 40sqm of floor).
(end quote)

Some thoughts about thermal mass are recorded in an earlier post at
http://www.ata.org.au/forums/topic/183
and at
http://www.ata.org.au/forums/topic/2272/page/2

My plan is to use fabric eaves over summer and remove them for each winter.

Posted Monday 18 Jul 2011 @ 1:03:57 pm from IP #
Danhug49
Member

For information purposes only, our company has a method now for putting double glazing into any window type. This is useful for anyone who already has standard windows and is thinking about upgrading. Its really an alternative to new windows (roughly $30,000) or secondary glazing (about $15,000). The retro fit will be about $8,000. Maybe an extra grand for a LowE version.

Posted Tuesday 19 Jul 2011 @ 3:38:34 am from IP #
TonyT
Member

Danhug49
Please will you provide more information, perhaps including the link to a website ?
Thanks
Tony

Posted Tuesday 19 Jul 2011 @ 8:04:54 am from IP #
dbindoff
Member

I renovated a kitchen recently and had to replace a large pane of plain glass - I elected to use comfortplus clear because of the lower U value. The pane receives winter sun and I have found that the passive solar gain is noticeably better (desirable) - and no UV also desirable)and the kitchen noticeably retains warmth better on cold nights.

So I am impressed so far, I have no experience in summer but shading should make it OK.

I looked at the economics of replacing other window panes but other options look better in that case for the money.

I found a window film called 'Ener Logic' which is sold in the US and I have been told Tint a Car will release it in Australia in September. Ener Logic claims to impart double glazed thermal performance to an existing single pane.

Posted Thursday 21 Jul 2011 @ 1:51:37 am from IP #
heftzwecke
Member

If I would build a new house I would not considering anything else than double glazed windows.
I come from a country were everything else is forbidden and this has a good reason. I would rather try to put less windows in, it's all a matter about planning. Never safe on quality because that is too expensive.

Posted Friday 22 Jul 2011 @ 9:07:19 am from IP #
simplelife
Member

Bundy wrote: "Hi there, I have had conflicting info on Low-e or Comfort Plus type glazing options. One Solar Architect who I do respect says that Normal 4mm glass has an R value of about 0.15 whilst this Low E glass has an R value of about 0.32 but costs significantly more (In our case approx 70% more than 6.83mm Laminiated glass) and he says it is not worth that extra cost. In his opinion Heavy drapes and pelmets work far better."

I have been reading up about double glazing vs single glazing vs low-e etc. and am amazed by how complicated it all is.

Is there ANYWHERE I can find a way of reading about my options, with price comparisons and discussions/case studies about the reality of upgrading? I have had 3 quotes now, from $8K to $24K for 4 windows only, with DG and argon gas, thermally broken timber/aluminium or timber only!

I do understand you get what you pay for, but I fail to see how I can justify that sort of price difference to regular glazing, just to upgrade from an R value of .15 to .32 using the above figures as an example.

Surely pelmets and curtains would do just as well, for a fraction of the price!

It makes me wonder if I'm better to put the cost difference into some more PV's on my roof and forget the DG.

Posted Tuesday 20 Mar 2012 @ 10:12:03 am from IP #
ferylberyl
Member

In reply to Simple Lifes quote: Surely pelmets and curtains would do just as well for a fraction of the price.

I have a 60's/70's brick veneer with a near flat roof, stuff all insulation (which thanks to installing solar power, water and a Solarventi there is not much chance of getting new insulation now!) and aluminium standard glass windows.
I recently got new roller blinds (about $100 each?) fitted inside the window frame believing that being closer to the glass these would help thermally. I subsequently discovered that they let in way too much light around the edges so would be absolutely useless at cutting heat loss / gain. So I put up the existing roller blinds that fit to the outside (inside?) of the window frame as well.
During the summer months I measured a 1-2 degree difference between the blinds.
Yesterday morning at 6am, about 6 degrees outside at a guess, there was a 2-2.5 degree difference between the blinds and up to 5 degrees between the glass and the innermost blind. Curtains as well add another 1-2 degrees depending on weight (even net curtains!)
Recently I finally got my act together and made pelmets for all windows. Put them up this morning and hoping they will also assist in keeping the heat in over the cold months to come.
To have double glazing......... 'tis but a dream I'm afraid.

Posted Tuesday 27 Mar 2012 @ 2:21:47 am from IP #
dlvb19
Member

SimpleLife,

Your probably spot on. This has been discussed in many other forums on this site with some amazing contributions by other members. Run a search.

In brief though:
On a new building I think its definitely worth it, but it sounds as if your considering an upgrade to existing windows.
Its a LOT of money to do a refit, I would suggest looking into commercially available films which I have surmised from ATA forum comments work quite well.
For about $200 you can get a "green" home assessment and will be told the best way to stop heat loss/gain or whatever your climate requires. This may involve plugging leaks, getting more insulation, window films, weather seals on doors/windows .etc.

At the end of the day if your home is already up to scratch you might want to take the plunge and do a full upgrade. If so I suggest Stegbar - they had the best price/perfomance ratio I could find...dont even bother with Parhammer...in your wildest fantasies.

On a different note I have noticed that when standing close to SG windows you can often feel the cold "radiating" (a big sorry to all the physicists) on your skin which is very unplesant. DG does not have this in my experience.

Also try Trend windows. Good luck

Posted Tuesday 27 Mar 2012 @ 5:46:28 am from IP #

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