Here is the long awaited post about my recycled HRV system. I have posted it under the subject title 'Insulation' because it is an important part of an energy efficient house. In cold weather we tend to close all the windows and door in an effort to keep the heat in. While this keeps us warm and conserves fuel, it leaves us breathing stale air. Houses built in colder climates have HRV installed as a matter of course. The system draws stale air from the rooms in the house and, in the HRV unit, transfers the heat from it to fresh air drawn in from outside. This way the house can have a few air changes each day with little loss of heat. The HRV unit that I saved from the skip is an older passive design. Here is a snap of it in its new home.
When the lid is off you can see the heat exchangers. I will show one of those in more detail later. I have marked the passage of air through the unit. The fresh (in blue) and stale (in red) air never mix. They are separated by multiple layers of aluminium foil through each exchanger. At the top of the box is a fan which forces the air through the system. This unit is about 75% efficient whereas a modern active one can be over 90% efficient. Beggers can't be choosers.
Here is a look through one of the heat exchangers. If we call the channels we can see the light through 'even', and say that the fresh air is being drawn through them, then the solid looking bars are the sides of the 'odd' channels through which the stale air is being drawn. A look at a corner view shows the 'even' and 'odd' idea better. I hope you can see that the two flows of air only touch each other through a huge surface area of aluminium foil. This is how the two flows are kept apart but the heat difference between them causes heat to flow from the warm stale air through the foil into the fresh colder air. The case is designed with rubber seals to ensure that the two flows are kept separate. There are washable filters on both inputs to the system.
Next I had to do the pipe work. this is a pic of the exhaust manifold. Pipes from each of the bedrooms and one from the bathroom are added together and ducted into the unit. In this manifold there is a valve which can be adjusted to give the bathroom priority if the humidity rises above a pre-determined level. This will be automatic when I work out how to do it! Keen eyed among you will notice that it has a distinctly DIY look about it.
There is a similar lash up of a manifold on the fresh air side. Here is a pic of the vents in one of the bedrooms. The whole setup has been salvaged from skips over the last few years. Even the cable ties that hold the ducts to the rafters, were taken from lamposts after the presidential election posters were removed. The only bought stuff was a length of 4" flexible extracter duct, a roll of foil tape and a tube of silicone sealant.
I don't know how you find this stuff, all I ever seem to find is busted plant pots and old paving slabs.
One question about your setup, how noisy is it, I have been in one house where they had one of these systems and it was totally quiet, and in another house that had a very low level hum (I think the fan wasn't aligned properly or a bearing was shot) that I found quite annoying.
Jim, I find it difficult to walk past a skip without taking a wee look. I also have a mental directory of where the good skips might be, industrial estates are a good bet. I take a tour of these when I am near by. Also it helps to have a good range of spoofs to hand when some begrudger comes along. I got one pile of air-con ducting out of a skip by telling the begrudger that I was cutting them up to make garden planters. He thought it was a great idea and wished me all the best. I am sure that If I had told him that I was doing a HRV setup on the cheap, he would have been much less helpful. So, to answer your question, skip dipping is an active business rather than one of chance. The fan in this unit is very big, 10" across When I tested it first, I plugged it into full voltage mains and it howled and would pull the hair-do off you. In normal use it runs slowly and is very quiet. When the bearings go in this unit I will pull it apart and replace them. They are standard components. conor
I never thought of it as 'an active business' before and I guess the skips I have looked in have been outside houses which increases the chances of the garden and builders rubble sort of stuff. I must check out some of the more industrial places and see what there is to see.
The house I mentioned with the humming HRV system was a fairly new house, probably a year or so old, I think it was probably a bad install job or a piece of kit that was dodgy to begin with rather than it wearing out. No one else seemed to be bothered by it but if I had lived in the house i'd have been howling at the moon in about 3 days.
I have an old book on air conditioning which I used as a guide for this installation. One of the most important aspects of the job is to use ducting of as large a diameter as is necessary to move the air quietly. Bends and reducers require careful consideration also. I had the ducting for this job in the yard for years so I designed my system around 6" pipe with 4" for the bathroom. I wonder what diameter was used in the system you suffered? conor