I did an article for Home Power on the Low Thermal Mass Sunspace concept — its in the Dec 2013 issue, which is just coming out.
William’s Minnesota LTMS
I’m a big fan of the Low Thermal Mass Sunspace (LTMS). In a nutshell, this is an attached sunspace in which the design is optimized for providing maximum heat to the attached house. The main design characteristics are:
Double glazing with tilt angle optimized for winter collection
Unglazed surfaces in the sunspace are dark in color to absorb sun well
Unglazed surfaces are well insulated to reduce heat loss
Unglazed surfaces are low in mass so that they don’t suck up heat you want to go to the house
A high capacity fan/duct system delivers heated air to the house as fast as the sunspace makes it
Some of this may seem strange at first compared to the usual sunspace design guides, but its all aimed at maximizing heat production and in getting as much of the heat as possible to the house.
It turns out that if you follow these design guides, the LTMS will produce heat for the house just as efficiently as a good commercial collector with the same glazed area — AND it will give you all the benefits of a sunspace as well. Benefits include: great place to have cup of coffee in the sun, great playroom or family hangout, all season clothes line drying, wood drying, …
About the only downside of the LTMS is that when the sun goes down it goes cold quickly, so its not a space to hang out in after sunset, or go grow plants in cold climates.
The performance is impressive. My test LTMS with 200 sf of glazing produced 200K BTU of heat for the house on one sunny winter day — equivalent to nearly 3 gallons of propane burned in a typical furnace.
The test LTMS under construction.
I also tested the performance of my test sunspace when it was closed in, but not insulated and with a dirt floor — in this configuration it only delivered 1/3 of the heat to the house than the finished sunspace with insulated low mass surfaces.
The finished test LTMS
I’ve done a section on LTMS’s that goes into quite a bit of detail on on the design, performance testing, and includes some great LTMS examples contributed by Mike, Nick, and William.
Mike’s example LTMS — heating the house and solar drying clothes!
Nick’s 3 story LTMS that provides most of the heat for his very difficult to heat old home.
The Home Power article covers everything in the LTMS section in one place and the Home Power editors have worked it into something that is clear, easy to read, and still quite detailed.
There is a lot of interest in solar air heating collectors that work with an existing window. One of the more popular ones has been the Mother Earth News Heat Grabber. These collectors don’t require punching new holes in your wall, are simple to build, and they can be seasonally installed.
This work is an attempt to go a step further with collectors that work in conjunction with an existing window. The hope is to both improve the aesthetics and to include more collector area.
Clearly there is plenty of room for improvement, so lets hear your ideas.
One think I want to make clear up front is that solar collectors that just fit over or in an existing window without increasing the collection area of the window do not work — they do not end up collecting any more heat than the window alone. There are kits out there for collectors that fit in the window — they are ineffective.
Collector on left window — regular window on right
This first cut prototype sits over the window and extends out to both sides and on the top and bottom. It increases the collection area from 12 sf for the window alone up to 45 sf — a pretty good increase in heat gathering area.
Outlet manifold on top supports screen absorber and pulls in the hot air across the collector width, and sends it down the vertical pipe and into the room The room air inlets are on the right and left at the bottom of the window.
Inside view — inlets on right and left — outlet with fan in middle.
Some of the outstanding questions…
How to make it look nicer and how to better integrate the collector with the house design
We have been working for the last few years on reducing our electricity use. So far we have cut our electricity use about in half using these projects. We started at right around 1000 KWH per month, and got down to right around 500 KWH per month using the simple projects listed above. We also did a 2.2 KW home built PV system that generates (on average) about 270 KWH a month, so our average electricity bill is around 250 KWH a month — 1/4 of what it was when we started.
But, one thing that has bugged me for several years is that our DISH DVR uses 53 watts all day every day day and night. This adds up to 464 KWH and 750 lbs of CO2 emissions a year — its actually more energy than our fridge uses. It is possible to turn it off at night, but then you lose any recordings that were to be made and have to wait through the boot up process in the morning. I’ve kept track of new DISH DVR offerings in the hope that they would address this problem, but, according to DISH, the power usage on the new offerings is about the same as the one I have.
It came to our attention that Direct TV has done some work on this problem with considerable success. Most of the DVRs they now offer are Energy Star compliant, and use far less power than our DVR. So, we decided to drop DISH (after 12 years) and go to Direct.
We ordered their Genie DVR which is a “whole house” DVR in that it will allow TV’s in different rooms to watch different shows. It also has 5 tuners and will record up to 5 shows at one time. So, the new DVR offers some feature gains as well as reduced power usage.
The power usage on the new DVR is 18 watts. Compared to the old DVR, this is a saving of 310 KWH and 500 lbs of CO2 emissions a year. All for a DVR with much more functionality than our old one.
New DVR on the Kill A Watt meter.
The new DVR also has a “sleep” feature in which after 4 hours of no activity it goes into a lower power consumption mode. In the few days we have had the DVR, I’ve not seen it go into this mode at all and the power consumption over the first few days as measured by the KillAWatt meter indicates that it is not spending any significant time in this mode. Perhaps shows recorded late at night kick it out of this mode? But, given that the base power usage is so low, it does not make a lot of difference.
The new receiver/DVR
Anyway, I guess the message is to check the power consumption of everything that uses power in your house — you may find that some of those innocent looking boxes are using a lot more energy than you think.