Another cheap 12kW Kingspan Aeromax ASHP

[Alexphd1]

@ProDave what size of heat pump are you looking for?

 

[ProDave]

2 minutes ago, Alexphd1 said:

@ProDave what size of heat pump are you looking for?

 

6-12KW should be plenty.

 

I am in no hurry. I won't be installing it for some time and cashflow is tight at the moment, so I would have bought this one at the right price, but if I have to pay anything approaching normal retail price, then it will have to wait.

[Inchbyinch]

@JSHarris

im about to start the install of this unit. I won't have solar PV (at the start But may retrofit) so I'll be heating a large buffer (500l) at the set flow rate and using this to preheat dhw with a plate heat exchanger before boosting with an in line heater. 

 

This based on your analysis that if PV wasn't feasible this was the most efficient way to heat a low energy house and get dhw

 

Ive two questions,

1) what is the temp loss through your plate heat exchanger and how would one size it

2) what do you think is the max circ temperature that will avoid defrosts?

 

thanks as ever

ed

[Jeremy Harris]

The temperature drop across the PHE depends on the relative flow rates and the plate area, but I worked out that the 44kW rated one I used was OK for well over 10 kW at the lower temperature that we're running at, and our ASHP is only rated at 7 kW.  The 44kW rating seems to be for a higher temperature differential and higher operating temperature, typically the sort of internal temperatures that combi boilers operate at (so maybe 70 deg C on the sealed primary, 55 deg C of the DHW secondary.  In your case, given the modest price difference, I would go for the 66 kW version:  http://www.wiltec.de/house-garden-pump-plate-heat-exchanger/plate-heat-exchangers-stainless-steel-cupper-brazed/hrale-stainless-steel-heat-excahnger-30-plates-plate-heat-exchanger-max-66-kw.html. 

 

In practice I've found that the temperature drop across the PHE rarely exceeds 2 deg C, so I'm sure my derating is a bit pessimistic.  Given that the 66 kW PHE is less than €10 more than the 44 kW one: http://www.wiltec.de/house-garden-pump-plate-heat-exchanger/plate-heat-exchangers-stainless-steel-cupper-brazed/hrale-stainless-steel-heat-exchanger-20-plates-plate-heat-exchanger-max-44-kw.html , there doesn't seem much point in going for one that might just about be OK.

 

I found  that the maximum flow temperature for our location and installation seems to be around 40 deg C.  Any higher then this and the unit starts to defrost in cool (around 3 to 4 deg C) weather when it happens to be fairly damp.  The worst case for frosting seems to be still, cool, misty days, the sort of weather where your car will have condensation over it in the morning.  Cold dry weather is fine, the risk of defrosting almost goes away as soon as the air temperature drops below freezing point.

 

As an extra bit of info, the 44 kW PHE we have had a pressure drop when running a shower at 10 litres/minute of slightly under 0.03 bar, which is so low as to be negligible (our incoming supply is at 3.5 bar, so this is less than 1% pressure drop).  The 66 kW PHE has a lower pressure drop; for a shower at 10 litres/minute the drop would be just under 0.02 bar.  We connected the smaller connections to the mains pressure DHW feed and the larger tappings to the circulating pump and buffer tank.

Edited September 7, 2017 by JSHarris
Added pressure drop info

[Inchbyinch]

@JSHarris outstanding as always. Based on the above and my situation would I be best to employ a reverse heat curve that slightly increases the cct temp with ambient....not sure is that possible. I think not. I might just increase the temp for the summer months to use the inline heater less. 

 

I promise I'll do a proper documented version of my house one of these days but with two under two and a full time job just to get the house built is more than I can muster. 

 

A side issue if I may, when looking at diodes and 12v relays etc...do you have the supplier you used? I was looking at these http://www.tme.eu/en/katalog/#id_category=100051&s_field=artykul&s_order=ASC&visible_params=2%2C2%2C693%2C914%2C915%2C916%2C925%2C925%2C938&used_params=2%3A45221%3B925%3A24610%3B

 

am I onthe right track? 

[Jeremy Harris]

You can programme the slope of the flow temperature versus ambient temperature with a bit of faffing about via the command unit, but I've found that just setting it for a flat 40 deg C seems to work OK. 

 

The relays I used were 12V ones, that plug in to DIN rail mount sockets, and have additional LED modules to show which relay is on.  The DIN rail socket fits into a small consumer unit type box (I bought a  cheap one with a clear cover so I could see the LEDs).  I powered the relays via a 12V Meanwell DIN rail mount power supply.

 

The relays I used were standard 12V  DIN rail mount sockets type ones, with the LED indicator modules, like these: http://www.ebay.co.uk/itm/RELAY-MODULE-2CO-12VDC-/172741730264?hash=item2838359fd8:g:r4cAAOSwgv5ZSlRh

 

The diodes were cheap 1N4001's soldered together with leads to wire up to the relay modules.  To allow easy connection of the external thermostat wiring I used DIN rail terminal blocks, like these: http://www.ebay.co.uk/itm/2-5MM-12-PIECE-DIN-TERM-PACK-/172750888899?hash=item2838c15fc3:g:s5IAAOSw8GtZUmeF these fitted behind areas of the consumer unit box where I hadn't punched out the front covers, to hide the terminals.

 

The Meanwell 12V power supply I used was one of these:http://www.ebay.co.uk/itm/Mean-Well-DR-15-12-12V-15W-Step-Shape-Din-Rail-PSU-/132076460496?hash=item1ec05ed9d0:g:anMAAOSwnHZYifqK (it needs to be the step shaped one to fit a consumer unit type housing, I think, and keep the terminals protected)

 

IIRC, I used a 9 module DIN housing, just a bare consumer unit type unit with no switches etc fitted, like this one: http://www.ebay.co.uk/itm/Consumer-Unit-enclosure-MCB-Fuses-box-coffret-electrique-5-9-13-18-26-module-way-/251353151094?var=&hash=item0

 

I can check tomorrow to be sure whether it's a 9 or 13 module box.

[Inchbyinch]

Great people come in many forms but Mr Harris you are certainly one of them. 

 

Thanks forall all of the above. I'll keep you posted. 

 

R Ed