Ideal head pressure using R22 on reverse cycle heating

Ideal head pressure using R22 on reverse cycle heating


I am currently designing a system and I wish advise on what would be the ideal head pressure using R22 for heating.

The cooling is is no problem but I wish to set up pressure switches so as to have the best possible head pressure for the system to be most efficient.

The condenser is a bit oversized and has multiple fans on it

The system has TX valves for both cooling and heating, plus a reciever so it has the ability to be able to be a bit flexable.

The system is in a fairly warm part of the country and so icing up will not be a problem.

As low as possible, whilst meeting its requirements

WOW sry for the typo.......What type of compressors are you running??If you get your head pressure to low you can increase the velocity thru the compressor can carry your oil out faster than you can get it back. There are a few other facts needed as well but as a rule of thumb on above freezing systems I set most 22 compressors by discharge temp. I look for a 75 degree climb above suction

Sry about the dbl post [That's OK, sorted now, Brian]

It is a reciprocating compressor and it does have an oil separatoron it plus a slop pot on the suction side of the compressor.
I am not looking for a low head pressure, rather one thatwill give me the most heat without straining the compressor, or causing otherproblems.

At the moment I am considering around about 300 PSIdischarge pressure when it is on reverse cycle.
That does come out about the 75 f above suction that youmention.

You may find some variations in what I type as here we usethe metric system and I need to convert them to imperial for these posts.

Bob, are you looking to heat, say, a pool? Can't believe you would want a reverse cycle A/C for home heating in Cairns Queensland. Reverse cycle A/c's for this area are limited to -5c ambient and your location will never breach that, so 300 PSI is as far as i would go. Cheers, Mike.

Quote:

---

Originally Posted by bob roberts

The cooling is is no problem but I wish to set up pressure switches so as to have the best possible head pressure for the system to be most efficient.

---

You dont get eficiency by seting pressure switches.
They are there to prevent compresor from working outside its allowable working envelope.

Eficieny is better when compresion ratio is smaller.
That mean use of heat exchangers with smaller TD and using low temperature heating like fan-coils or even better floor heating.
Oversized condenser is plus as evaporator in heating mode but it need fan speed control for warmer days to prevent compresor from overloading.

Quote:

---

Originally Posted by Mark Selby

If you get your head pressure to low you can increase the velocity thru the compressor can carry your oil out faster than you can get it back.

---

Hi Mark,

Should that read if head pressure is too high velocity is increased carrying out oil?
Not trying to split hairs but I thought the oil carry out scenario worsened with greater pressure difference between suction and discharge.

Cheers,
Andy.

No the system is not for a pool it is for air conditioning.Last night it went down to 15 c (59 f), and personally I felt cold. Once you live in the tropics you getacclimatized to the warmer weather, and notice it when it cools down. Heretwice in 9 years I have seen it drop to 9 c (48 f) but most years about 11 c(51 f) is as cold as it gets in the cooler season.

The pressure switches will control the condeser fans which will corntol the head pressure.

If the head pressure gets too high the pressure switch will shut off a condser fan to control the amout of refrigerant being boiled off in the condenser (outside coil).

These pressure switches are not the hi/lo pressures switched used on the compressor.

Quote:

---

Originally Posted by bob roberts

The pressure switches will control the condenser fans which will control the head pressure.

If the head pressure gets too high the pressure switch will shut off a condenser fan to control the amount of refrigerant being boiled off in the condenser (outside coil).

---

If you shut off a fan when the pressure/temperature rises then the head pressure will just get higher.

You are wrong my friend. When pressure switch turn off fan on what he call "condenser" which is actualy evaporator in reverse cycle, load will reduce and pressure on high side will fall.

But, I would recomend much better control with fan speed controler guided by pressure sensor.
Like Carel Microchiller 2.

I accept that Nike as long as that is what he is doing.

Quote:

---

Originally Posted by bob roberts

No the system is not for a pool it is for air conditioning.Last night it went down to 15 c (59 f), and personally I felt cold. Once you live in the tropics you getacclimatized to the warmer weather, and notice it when it cools down. Heretwice in 9 years I have seen it drop to 9 c (48 f) but most years about 11 c(51 f) is as cold as it gets in the cooler season.

---

Nice place at this time of the year to visit, Bob. With the a/c, so long as the suction pressure does not exceed say, 70PSI when on reverse cycle, it should run sweet. Had my a/c on last night as we're getting close to frost conditions on the hills behind you.:eek:.. mike.

>>If you shut off a fan when the pressure/temperature rises then the head pressure will just get higher. <<


I am talking of shutting off condenser fans while the unit ison heating so it will reduce the suction pressure, thus reduce the headpressure.

IE the condenser fan will be in fact an evaporator fan whilethe system is on heating.

>>Nice place at this time of the year to visit, Bob. With the a/c, so long as the suction pressure does not exceed say, 70PSI when on reverse cycle, it should run sweet. Had my a/c on last night as we're getting close to frost conditions on the hills behind you<<


It gets cold in them there hills, I know having visited afriend in Herberton when the weather was cooler.......

I think I have seen temperature on the tablelands at -6 c(21 f) a bit too cool for me.

I do not think one would get much heat out of a reversecycle system at those temperatures... :-)

>>You are wrong my friend. When pressure switch turn off fan on what he call "condenser" which is actualy evaporator in reverse cycle, load will reduce and pressure on high side will fall.

But, I would recomend much better control with fan speed controler guided by pressure sensor.
Like Carel Microchiller 2. <<

I already do have a speed control fitted for the cooling side, but I have not seen one that will work for heating, I will check the suppliers and see what they say.

I agree it is a better system, but it will depend if they are available.

You could use this one
http://www.danfoss.com/North_America...ed+Control.htm