Digital Scrolls

[MikeHolm]

OK, I know some of this has been covered before but I can't find it (CM always seems to be able to) but can anyone think of a reason NOT to use a digital scroll on a heat pump with an appropriately sized storage tank?

Design info seems a bit lacking it seems as well.

[chillerman2006]

Hi Mike

does this answer your question mate

We are taliking about water heating units that are used for static heating devices (rads and underfloor) so by pure nature is slow reacting, so quick response in temperature is just not required, I really can see a point for an inverter for this applicaqtion, at 10 starts an hours 6 mins off period on stastic heat exchanger will not change the feel of a home. (air to air systems with forced draft heating, inverter is required 100%)

R's chillerman

[MikeHolm]

Yes, but the "reported advantage" by Copeland (for heating) of a digital scroll (not an inverter) is better low ambient performance over a single stage unit, and they state this advantage for ASHPs with a water storage!!!!!

[chillerman2006]

Argh I see

running at part load in low ambients will decrease mass flow through the outdoor evap

allowing more time for heat to be absorbed

made up figures for example

if at 0*c x amount of heat is added to refrigerant in evap at full load

and at full load you have 1kg of refrigerant passing through evap per minute

then at half load you have half kg of refrigerant passing through evap per minute

you add more heat to that half kg increasing suction pressure/temp

which in turn increases head pressure/temp

if suction pressure/temp remains too low

you will not gain enough head pressure/temp to heat the water to desired temp

R's chillerman

[chemi-cool]

Why digital scroll? ZB will do the job just as good and at a lower price.
Can you add HGB to keep the evaporator temp above 0C?

[chillerman2006]

Why digital scroll? ZB will do the job just as good and at a lower price.
Can you add HGB to keep the evaporator temp above 0C?

Hi Chemi

good point mate, hot gas bypass would do the same job nicely

so still looks like Mike no need for digi mate

just copeland sales pitch

R's chillerman

[MikeHolm]

Just asking guys.....doesn't mean I believe them.

Isn't HGB a bit of an energy waster though?....Ambient to be concerned with is -15C

I think Mad would shoot me if i used HGB, may BigFreeze would too.

[chillerman2006]

Argh you got me now Mike

if Mad would shoot you for using hgb, I'm not arguing

he could be bigger than me and may be bumping into him soon

and thinking about it

you transfer energy to heat and then dump it back into low side with out using it to make hot water

just to increase heat/mass hmmmm .... yeah does not sound economical when looking for efficient heat pump

God Mr mike - you getting me thinking tonight and Mad will probaly turn up soon and say I got it all wrong

R's chillerman

[MikeHolm]

He might tell me Chemi is spot on as well.....I must defer to my superiors on this and that is all you regulars...

Come on Mad, chime in.....

[chillerman2006]

Mike

Gary has also shown me recently along with DesA

they all have an in depth understanding of heat/energy and efficient use

which is all based around

energy can niether be created or destroyed but transfered from one form to another

as the heat has to be transfered from energy and not transfered from ambient

when using hgb, it does appear your argument is justified with digital scrolls at -15

they probaly all on holiday for a week or two and we be left wondering till then

[MikeHolm]

we shall see if more of the jedi masters chime in.....I would like to have this discussion as i seldom hear anyone talk about them. Most of the talk is about inverters which I agree makes no sense in heating a big tank of water.

[mad fridgie]

The simply question is "do you need close control of your water".

[MikeHolm]

Nope, you don't need close control of your water.....but the question is " given components of the same size, will the digital actually have a lower running cost then the ZB at -15C" or is it just that they believe the comp size can be reduced giving a lower running cost"

[Bigfreeze]

Wouldn't using a bigger evap on a static control unit give you the same result except for 100% of the time?
An offloading digital scroll could be more than likely become undersized for the application when dropped to 75% load in winter running.

[chillerman2006]

Hi BigFreeze

a larger evap would still give you the same heat transfer to a kg of refrigerant

you need to either control mass flow (reduce it to increase transfered heat per kg)

Or use another method such as hgb to increase mass/temp at compressor inlet at low ambients

R's chillerman