Wednesday, August 18, 2010

Absorption Chillers, Einstein refridgerators and cool stuff like that

Check out this Youtube TED video on a low-cost, high-tech refridgeration technology by Adam Grosser;
Crazy cool stuff - use a campfire as an energy source for cooling 3 gallons of water down to just above 0deg C, for 24hrs, in a 30deg C environment.  Funny thing is that to figure out this technology, they had to get the entire thermodynamics dept at Stanford involved and used CFD (computational fluid dynamics) to regenerate the property tables for ammonia, discovering that the old ones were all wrong.....this is pretty freaky stuff.

So, we need something that takes energy from the sun to power an absorption chiller designed to cool down a house.

Alternative:  Take the heat from inside the house (via the ERV/HRV), concentrate it to use as a heat source to power the absorption chiller to cool the house (again via ERV/HRV).  Any losses in efficiencies (waste heat) go to the domestic hot water system.  How cool would that be?
The Einstein refridgerator (an absorption chiller variant) uses no moving parts.  A guy named M. McCulloch is involved with reviving this technology at Oxford university.

Now the search for practical units in the marketplace begins.


Friday, August 13, 2010

Hot Water and Heating with Heat pumps

Using only electricity for DHW and heat on our project results in a primary energy consumption of some 180kWh/m^2an, so this simplest of solutions is definitely not passive house.  Using heat pumps exclusively for both cuts the number in half (the limit is 120kWh...).

There are many types of heat pump module available.  Therma-Vent, Aqua-Plus, Heat Harvester, HotPlate...  The issue is heat pumps degrade in COP significantly as the output temperatures reach 55 to 60deg C for DHW (but they can still do this with a COP of about 2).

Anyway, we need to look at harvesting the incoming ventilation air heat in summer and the outgoing ventilation air heat in summer, and the outgoing ventilation air heat in winter - got that?

The other thing is to integrate this all with solar thermal, and a 600' 3/4" pex loop in the ground should provide a fair bit of the needed energy as well.  It would be nice to have an insulated concrete tank where we can dump excess heat in summer and recover it in winter.  The earthtube seems more and more of an impracticality, though it is still a minor possibility.

Windows again

Had another conversation with Thermotech.  They confirmed the use of the zeros (apparently PHIUS is in agreement with this) in the PHPP for Psi spacer and Psi installation.  This makes a huge difference to the energy calculations reducing specific annual energy by a kWh/m^2 or more.
Also the cost of their windows with the 322Gain+ triple pane glass is about $65-70/SF depending on options.  The windows come with or without installation flanges, with or without brick mold.
No tilt and slide patio doors available - so this is an issue, since I don't want to pay shipping from europe for just a couple of doors.

Wednesday, August 4, 2010

Windows - Thermotech vs Others in PHPP

I went through detailed modelling of the thermal envelope recently and compared Thermotech windows to Euro-style PH windows:
Here's an email I sent to Stephen Thwaites of Thermotech about the results:

Dear Stephen and Ken,


Our design is a 2.5 storey house 41.5ft e-w by 36.5ft n-s. It is a rectangualr box with a gable roof, the ends facing e-w. Very simple and compact shape, with basement. 35 Openings totalling 39.9Sq m of windows, including 4 doors with 1/2 lites and including door and window frames, 20.9 sqm of that on the south.

What I found is:

1. Compared Thermotech glass to a high-performance 'Low-E 0.51 Neutralite Guardian Luxguard (item 35 in the PHPP)' glass with SHGC 0.51 and Ug 0.51, the model showed a 1kWh/m^2an advantage over the Thermotech 322Gain+(75/68) glass. With Thermotech glass, we were at 12.966kWh, and with the Neuatrilite, it was down to 11.99. This compares to the 15kWh/m^2an threshold to be a passive house. The comparison was done with the Thermotech casement frames in the model.

2. Returning the model to the Thermotech glass, I compared Thermotech frames to Optiwin Solarfassade frames, but keeping the 4 doors as before, which are generic. The narrowness of the Thermotech frames (0.68m compared to Optiwin's 0.100) is definitely a significant boost to performance.  Switching from Thermotech Casements all around to the Optiwin degraded the building's performance from 12.97kWh/m^2an to 14.81 - a very significant difference. Fixed (non opening) Thermotech windows will be good as well, of course, though there is still more comparing to do.
I didn't look at the sliding glass doors since I don't think they'll meet airtightness needs without the lift and slide hardware.