heat pump performance

[rbartlett]

hi guy's

seeing a lot of hp's struggling these days

I fear this is due to salesmen quoting the spec tight for cooling to get the job but then leaving the system low on heat performance -esp in near zero conditions

anyone else ??

cheers

richard

[rbartlett]

Some of them missing low ambient temp:D . kit...........


i'm concerned with their heating performance not cooling

cheers

richard

[slingblade]

Some of them missing low ambient temp . kit...........

WTF? what kind of talk is that? if you were 1/10 the man that marc o'brien is then your response would not consist of nonsense. please read this marc and help us all to understand with 6 or 7 hundred words of free wisdom from the one true source of south african perfection. i look forward to an in depth and technically sound perception of the problem related to a heat pump that provides poor duty when it is -5 deg. c outdoors

[lonesurvivor]

Well said:)

[Jez]

I fear this is due to salesmen quoting the spec tight for cooling to get the job but then leaving the system low on heat performance -esp in near zero conditions


To be fair the heating requirements for AC are very rarely calculated or supplied to size against, so it does not surprise me that systems are struggling in real conditions.

[frank]

hi guy's

seeing a lot of hp's struggling these days

I fear this is due to salesmen quoting the spec tight for cooling to get the job but then leaving the system low on heat performance -esp in near zero conditions

Are we talking LG? :)

[rbartlett]

mostly Frank to be fair..

cheers

richard

[stan1488]

from day 1 heat pumps were designed with supplementary heat sources to deal with extreme weather conditions, etc due primarly as you know to the lower air supply temps compared to say gas furnace , electric strip heat etc, sure you are already aware of these simple facts ;) cheers Richard , keep it simple to keep it cool, respectfully stan Z

[rbartlett]

from day 1 heat pumps were designed with supplementary heat sources to deal with extreme weather conditions, etc due primarly as you know to the lower air supply temps compared to say gas furnace , electric strip heat etc, sure you are already aware of these simple facts ;) cheers Richard , keep it simple to keep it cool, respectfully stan Z


stan

up to the mid/late '90's most a/c either came with electric heaters or the option. now most manufacturers 'rate' to -15c that option has been deleted.

cheers

richard

[Peter_1]

Sure, they're rated till -15°C but that's just the problem if you don't take care in selection.
I see this fault many times.

In Belgium, like i any other country there is a standard for calculation the needed heat capacity in a house.
This standard says that you have to calculate for an outside temperature of -10°C.
Say you need 15 kW.

What are many techs doing now: they look in the pricelist and they're looking for a HP of 14 kW.

In most pricelists, not the more sophisticated technical manual with capacities at different conditions, they select a machine with a cooling capacity of 15 kW and a heating capacity of 15kW. (most catalogs state 15 kW/15kW.)

This is looking for troubles because we all know :D that these capacities are given for an outside temperature of 7°C.

If you look then in the technical manuals for the capacities at -5°C to -7°C like we have here the last weeks, then it decreases almost by 2 if you take in account the many defrost cycles you need in these humid days.

[Jez]

At -15°C a heat pump system without electric boost will give approx. 50% of the published heating capacity. At typical UK winter design conditions (-5°C, 100% RH) a 35% drop in performance can be expected.

[Peter_1]

35% less..ok....but what with the SEER factor when you need to defrost every 2 hours or even every hour?
A huge drop if you ask me, especially if you know that some brands switch on electrical heaters. What a savings :)

But, there is a much larger reduction then 35%

Thermodynamically seen, this 35% isn't even correct:
take for example a Bitzer 2CC-4.2Y-40S, evaporating at7°C/45°C (standard aircoconditiong ratings) gives a heating capacity of 19.44 kW

Same compressor, same condensing temperature, outside temperature drops to -7°C where the evaporating temperature stabilises at -12°C.
Gives you a heating capacity of 10.88 kW

If evaporating at -10°C, then you have a heating capacity of 11.63 kW.

A lot more then 35% when in heating mode, when defrosting loosing how much.... 150%....?

Put once these figures in Coolpack, almost same results.

Don't believe always the figures of the airco manufacturers.

[slingblade]

Indeed, Magic, with heatpumps a supplementary heating kit is sometimes required for the lower temperatures.

However, at the outset, a salesman must decide whether to size the system for heating or cooling. That is to say the salesman must consider first whether heating is also a requirement and secondly, if so, then is the heating load less or greater than the cooling load.

In the UK south it almost always works out that the heating load is a mere fraction of the cooling load. That is to say that it is very rare the heating load exceeds the cooling load.

you disapoint me marc. the use of extra heaters is by its very nature related to the indoor section of a split type air conditioner. a low ambient kit would be relevant only to the outdoor unit as the low ambient temperature would be outside. you seem to have missed the point of the original question asked and the nonsensical response posed by mrcoolingmagic. the difference in required load between summer cooling and winter heating is very possibly not taken into account by the respective salesman to any inefficient system, but you have not explained the relationship of low temp. to poor duty. i hoped for so much more from you and fear now you are not the much respected technical rottweiler you make yourself out to be. mate.