BS: Heat exchangers

Subject: BS: Heat exchangers
From: Ed T
Date: 10 Nov 10 - 05:02 PM

I just had a mini split heeat exchanger (air inverter type) installed.It extracts heat from the air in colder times and air conditions in the warmer times. It is a back up,for comfort, not my main heat source. It is a 20 SEER model (Energy Star rated) and operates on 15 amps.

It is pump'in out a good amount heat now, Anyone have any experience with them?

Subject: RE: BS: Heat exchangers
From: Jack the Sailor
Date: 10 Nov 10 - 05:11 PM

We have a heat pump. Works fine in Coastal NC. Power bills are reasonable.

Subject: RE: BS: Heat exchangers
From: Donuel
Date: 10 Nov 10 - 07:09 PM

If one were to build a large exchanger 15 feet underground and use sodium the efficiency would be enough to heat large homes even in PA.
The electricity it uses for the pump could be renewable from solar and wind.

A Slowly leaking underground tank, slut for short, is however an enviormental concern.

Subject: RE: BS: Heat exchangers
From: Black belt caterpillar wrestler
Date: 11 Nov 10 - 07:58 AM

My concern is that in the conditions when it is most needed is also when it is most in-efficient.

We looked at ground-source and found that we would have problems with land drains that would freeze if we used trenches and boreholes could compromise our drinking water source borehole, so decided that air-source would be best, but not quite good enough.

We ended up spending our money on a wind turbine instead.

Subject: RE: BS: Heat exchangers
From: MarkS
Date: 11 Nov 10 - 08:29 AM

"We ended up spending our money on a wind turbine instead"

Can you offer some details about the type of turbine you installed?
Mrs. and I are thinking about doing the same and would love to have a user review.
Thanks
Mark

Subject: RE: BS: Heat exchangers
From: Black belt caterpillar wrestler
Date: 11 Nov 10 - 09:11 AM

We went through a firm called Sustainable Energy from just outside Preston and have a 5kw machine, an Iskra.
We have not had it that long so can't say whether the output will be what was forecast yet, but it looks like it will pay for itself within 10 years.
We chose it over a 6kw Proven as it will generate at a lower wind speed, and we hope generate more in the long run.

Things to take in to account:-
Planning permission for us was for 20 years, after that we have to apply again.
Needs to be 30m or so from any dwelling.
Feed in tarrifs may change, so the costs may change.
In high winds you may not get the full output as it will throttle back to protect itself (tested up to 130mph).

We have had a lightning strike which fried the rectifier and shut it down for a few days. We also had a failure of a slip ring which the firm are most upset about as it is supposed to be military quality!

The noise is about the same level as having a tree in the same location, except that the tower has a resonant frequency that makes a noise when it's generating about 900w.

See if you can go to an open day at an owner's site, that's what we did.

Subject: RE: BS: Heat exchangers
From: Stilly River Sage
Date: 11 Nov 10 - 12:25 PM

I put two heat pumps in this house so I have distinct zones and don't have to heat or cool the entire house. And for winter there is an auxiliary heater to add to what the pump itself generates. It works fine, it's the price of power that kills us here. I resolved last year to examine the rates every 12 months and move companies if I can find a better rate. My bills dropped considerably when I left that company that I'd been using since I moved into this house. Should have made the change a long time ago.

SRS

Subject: RE: BS: Heat exchangers
From: MarkS
Date: 11 Nov 10 - 07:27 PM

Black

Thank you - this type of info is most helpful

Mark

Subject: RE: BS: Heat exchangers
From: Black belt caterpillar wrestler
Date: 12 Nov 10 - 04:42 AM

I don't know where you are but for the UK consider these points as well.

Search for the nation wind speed database. This will tell you the average wind speed in your kilometre square. You may be able to guess whether your particular plot is better or worse than the figure given for the area. We are at 1100 feet up in the Lancashire Pennines on an open hill side with no trees to cause shelter or turbulence with a 12m tower but it is very revealing to notice how much the wind power varies over even a few seconds. We are on a slope of about 10 degrees and about 250 feet below the summit but we only have an arc of about 30 degrees of wind direction where there seems to be any sheltering effect.


How it works for us.
The turbine generates power as Alternating Current (A/C) but the frequency it generates it at is not fixed as it depends upon the wind speed etc. This is sent down a cable to the house where it is fed into the rectifier which converts it to Direct Current (D/C). This is a much more dangerous commodity as A/C will generally throw you away from it in an electrical shock situation whereas D/C will make your muscles clamp on to it.
The rectifier is linked by some short cables to a pair of "Windy Boy" inverter boxes (they can only cope with 2.5kw each). These have various programmable controls built into them and they convert the power back to A/C but at the correct frequency for the National Grid. These boxes are pretty efficient but have a radiator heat-sink on top of each one as there is some heat loss (happily we have them in a position where they will help prevent some pipes freezing in winter!). They've not got too hot to touch yet, rather like a nice hot water bottle temperature at most.
The power next goes to the NEDL meter which gives you a cumulative total for the power that you have generated. This is the one that gives you the readings that you send off to claim the Feed in Tariff (FIT) payments.
After this the power goes in to your consumer unit ( the box with all the fuses etc.). The clever thing is that the inverters arrange it so that the voltage of the power from the turbine is a few volts above that of the mains from the grid. This means that the power from the turbine is used first and until you are using all the power available from the turbine your normal electricity meter will not be changing.
There are a couple of isolator switches in the circuits, to cut off the power from the turbine and to cut the system off from the normal set up.
Your electrical supplier is normally the one who pays you your FITs. They also pay you for the power that you generate but don't use and feed back into the grid. This could be done via another meter but this cost a bit, so, for installations under about 10kw, they make the assumption that you feed half of what you generate into the grid.
This is paid at 3p per kwh so it's effectively 1.5p for every kwh you generate.
So you get 26.7p per kwh as FIT and 1.5p per kwh on top of this.

If there is a power cut on the National grid your turbine has to automatically stop generating as well. This is to protect anyone trying to repair the grid.

The wind varies year by year. Our neighbour has a Proven turbine and in the last three years this has generated 17,000, 17,000 and 13,000 kwh. So last year has been comparatively quiet.

The big commercial turbines are arranged so that they revolve at the right speed to produce power at the right frequency for the grid. This means that they don't start up until the wind is blowing hard enough, and they are driven up to speed. By this time the wind could have dropped again and they've actually used power over-all!

There is a lightning conductor on the tower but we still had enough power pass down the cable to fry the rectifier when it got hit. We also have a black square where the telephone socket used to be and a tree in the garden was not hit, but its support post had the top foot exploded and the strike travelled down and along the ground where the tree roots were close to the surface and blasted the turf off the top of them. We also had the inner layer of a double glazed window crack because of the sound blast.

Look at the economy seven tariffs and see if you can use power overnight cheaper.
If you are generating enough switch on an immersion heater. You get paid anyway so why not use the power?

We also thought about photovoltaic solar panels.

In their favour they do not need planning permission.

You do better with a roof facing in the right direction and the right slope, but you might get a fair amount despite this.

They cost more but the FITs are much bigger, however a change of government policy could alter these.

You don't have the other dwelling distance problem with panels.

They generate D/C which has to have inverters as for the turbine, but you might need a longer cable carrying the D/C. There are more losses in D/C circuits than A/C and, as mentioned above, it is more dangerous.

Usual size of panel installation is about 2kw for about £10,000. A turbine is about £25,000 for 5kw so there is not a lot of difference in outlay in proportion.

We used Sustainable Energy who have been pretty good, but another neighbour is using another company and having delays in getting anywhere.

In my opinion the Iskra ( named Evance now) is a better engineering solution than the Proven and these seem the best for our circumstances.

If you live in an area with a lot of turbulence and wind-shade etc. consider a vertical axis turbine. These look like glorified rotary washing lines and don't care what direction the wind is coming from.

Hope this all helps, but it could just give you information overload!

Subject: RE: BS: Heat exchangers
From: Black belt caterpillar wrestler
Date: 12 Nov 10 - 07:31 AM

Something that I would consider a heat-exchanger for is to recover heat from moist air expelled from bathrooms and kitchens.

There is quite a lot of info on this idea if you search for it. Basically you extract warm wet air from your bathroom/shower/cooker hood and get take the heat out and use it to warm up some dry air from outside, usually taking it from the loft space.

I have been to a lecture for landlords some years ago that was to do with creating positive pressure in a house, taking the dry air from the loft and using a slow pressure slow running fan to push it into the house. The idea was to keep the air in the house drier and so reduce condensation and mould.

As the air is colder outside it cannot have so much water vapour held in it and is thus drier than the air inside the house, which is warmer and thus can hold more. The air inside will be picking up water from lots of sources within the house, cooking, baths, showers etc.

Combine this with a heat exchanger and you are re-claiming the heat that you have already paid for.

I have this on my plans for when I've done everything else already on my DIY list!

Subject: RE: BS: Heat exchangers
From: GUEST,Guest from Sanity
Date: 12 Nov 10 - 11:48 AM

"Heat exchangers"......Great sex????

GfS