Charging calculation

[refcon32]

Hi all,

could someone tell me the calculation for pipe runs to see how much refrigerant goes into a a Denco D8A R407c.

[Brian_UK]

Couldn't find any precharge data for a Denco unit only superheat, sub-cooling and discharge superheat requirements.

There should be a data plate showing the initial and top-up charge on the unit from when it was commissioned.

[refcon32]

Couldn't find any precharge data for a Denco unit only superheat, sib-cooling and discharge superheat requirements.

There should be a data plate showing the initial and top-up charge on the unit from when it was commissioned.

Thanks Brian,
The usual, units are not marked up with charge and no commisioning dats on site. I will just have to work it out.
Pretty sure it was A Lennox unit I was working on years before and they had a calculation for your pipe size x ?kg per metre. Thought there might have been a recommendation and just trim the final charge.

[Brian_UK]

Having trouble getting Flakt/Denco site tonight, this data is from a download I did the other night relating to multi units running on R410a, only a guideline though.

Commissioning refrigerant circuits NOTE! When commissioning a refrigerant circuit for a Multi-DENCO unit it is important that the compressors are operating at a high speed. Once the high speed is achieved, time should be allowed for the system to stabilise.
Consideration and Targets
Below are the commissioning targets for an optimum system charge:
Superheat: 7 - 9 K (Default set point = 8 K)
Sub-cooling: 5 - 8 K
Discharge superheat: Compressor(s) at Low Speeds (< 50 RPS) = 15 - 25K
Compressor(s) at High Speeds (> 50 RPS) = 25 - 35K
NOTE! If fitted, it is important to consider the state of BOTH compressor speeds to understand the unit's operating level. For example, an inverter compressor may be operating at low speeds (< 50 RPS), but if the other compressor is active then the unit will be operating at above 50% capacity. Compressor speeds can be viewed in the 'Engineering level' of the C5-12 controller display. All 3 of these variables must be considered together for a successful commissioning.
You must also consider/witness what these variables will be at different operating conditions (e.g. low demand vs high demand).
++
It also says to check the sight glass in front of the TEV.

Good luck with it.

[refcon32]

Thanks for this Brian, I will keep this data for future reference got a good few of these units on various sites
Having trouble getting Flakt/Denco site tonight, this data is from a download I did the other night relating to multi units running on R410a, only a guideline though.

Commissioning refrigerant circuits NOTE! When commissioning a refrigerant circuit for a Multi-DENCO unit it is important that the compressors are operating at a high speed. Once the high speed is achieved, time should be allowed for the system to stabilise.
Consideration and Targets
Below are the commissioning targets for an optimum system charge:
Superheat: 7 - 9 K (Default set point = 8 K)
Sub-cooling: 5 - 8 K
Discharge superheat: Compressor(s) at Low Speeds (< 50 RPS) = 15 - 25K
Compressor(s) at High Speeds (> 50 RPS) = 25 - 35K
NOTE! If fitted, it is important to consider the state of BOTH compressor speeds to understand the unit's operating level. For example, an inverter compressor may be operating at low speeds (< 50 RPS), but if the other compressor is active then the unit will be operating at above 50% capacity. Compressor speeds can be viewed in the 'Engineering level' of the C5-12 controller display. All 3 of these variables must be considered together for a successful commissioning.
You must also consider/witness what these variables will be at different operating conditions (e.g. low demand vs high demand).
++
It also says to check the sight glass in front of the TEV.

Good luck with it.

[nike123]

If you have liquid receiver in that unit, than you could simply assume that manufacturer has sized it properly and that total system charge (by liquid volume) is no more than 70-75% of volume of that receiver as starting point

http://www.carly-sa.com/How-to-choose-the-size-of-a-liquid.html

Than you should use that volume for calculating weight of refrigerant.
You could use Coolpack software for your calculations of refrigerant density at certain liquid temperature and also liquid pipe volumes. Also since gas phase of refrigerant is few hundreds times lighter than liquid phase it could be neglected in this calculation.

https://www.ipu.dk/products/coolpack/