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Recent content by marcoh

  1. marcoh

    undersized ac vs room temperature

    reset the room temperature in your heat load software until you get a sensible cooling load of 103kW, noting you need to also check the change in sensible capacity as air-on conditions change. But then read ANSI/AHRI STANDARD 210/240-2008 "Performance Rating of Unitary Air-Conditioning &...
  2. marcoh

    Shelf Life / Storage life of Refrigerant

    I would have though forever as well. The cylinder is full of refrigerant, so there is nothing to contaminate it, and you could not get a better storage system
  3. marcoh

    psychrometric chart question

    Yes you can do it on a psych chart. Find you starting point with the dry bulb and moisture and simply draw the enthalpy line up front that point. If you psych chart does not show the enthalpy marks you might need to get a better chart.....
  4. marcoh

    Cooling Tower Equalizing Line

    It does all come to the mighty $$$ but an effective SSF system will reduce cleaning requirements for the cooling towers and the cleaner fill will enable cooler water into the chillers, thus reducing chiller energy consumption. But to put a hard cost to these is not easy.
  5. marcoh

    Safety Factor in Hyraulic Calculations for Chilled Water Loop

    For a 20 storey tower you will have multiple chillers and multiple pumps. You pumps should match the chiller capacity which may or may not be the same as the connected AHU load. Personally I would put the safety factor into the the AHU's and size the chillers/pumps flow rate to the calculated...
  6. marcoh

    Hvac system in hot and humid climate

    No issue with using VRF but you must use one of their outside air preconditioning units to mainly remove moisture from the outside air. If you do not use an outside air preconditioned you will have RH issues as the standard VRF FCU's cannot handle significant latent loads. If you have...
  7. marcoh

    Cooling Tower Blowdown Best Practice

    Blowdown should be between the cooling tower outlet and the chemical treatment connection so you don't waste all your expensive chemicals before they have a chance to do their work. You should also have a side stream filtration system to remove solids from the water.
  8. marcoh

    Not Cold Enough in Tuberculosis Lab

    First check you airflow to make sure you are getting the airflow you required and at the same time measure your supply air temperature. I would suggest the AC is grossly oversized and is limited to the number of starts/hour.
  9. marcoh

    Cooling Tower Equalizing Line

    You should have a side stream filtration system for cooling towers and then connect the SSF suction to the balancing line which will ensure there is always water flowing through the balancing line.
  10. marcoh

    Generator room ventilation

    If you have a genset with a remote radiator you will still need an enormous amount of ventilation air to cool the generator room. I recently did a generator room with two 2000kVa water cooled generators and required 25,000L/s ventilation to maintain a 18 degree temperature rise in the room over...
  11. marcoh

    High Rise Stair Pressurisation

    6.5 m/s should be fine and using a concrete shaft is fine and no need to metal duct. Normally the fire stair is within a concrete core so use the concrete core for 3 sides of your riser and construct the wall between the stair and riser. Therefore any leakage will be into the stairs. I would...
  12. marcoh

    Variable Primary Flow CHW and chiller interaction

    I would suggest always use mag flow meters to measure the primary and building flow rates. Use the actual building flow demand to stage the chillers, and the primary flow meter to control the bypass valve. Pumps speed is controlled by a dP in the field near furtherest AHU to maintain th...
  13. marcoh

    Data Center Humidity Control

    All depends on where in the world you are and ambient climate. Locate the data centre north of the arctic circle and you could have nil mechanical cooling or dehumidification requirements. Assumption you cannot relocate, the next biggest question is the size of the data centre. Especially if...
  14. marcoh

    Health Care - Negative Isolation Rooms.

    Most isolation rooms I have seen are based on 12ACH supply air, exhaust is oversized by about 20%, and the the exhaust is balanced at commissioning to achieve the required pressure differential.
  15. marcoh

    High Rise Stair Pressurisation

    All depends on how you have sized your shafts. I have done similar buildings with one set of fan and worked fine. Control of multiple fans can become a much bigger issue, especially when trying to maintain acceptable door pressures.
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