To Keep Docs Cool, Dry and Happy

Transcription

1 To Keep Docs Cool, Dry and Happy David N. Schurk DES., CEM., LEED-AP., CDSM., SFP., CWEP. Director of Healthcare Accounts for Heat Transfer Solutions in Houston, TX.

2 Learning Objectives 1. Understand the roll that both temperature and humidity play in proving doctor and patient comfort. 2. Learn what dew-point temperature is, how its measured and maintained, and why its key to producing satisfactory operating room conditions. 3. Discover how to reference a psychrometric chart (or App) to quickly determine space temperature and humidity conditions. 4. Learn to assess existing HVAC systems and determine if they are capable of producing space temperature/humidity conditions needed. 5. Understand the pros and cons of all three common cooling and dehumidification equipment types installed in hospitals today, DX cooling, medium and low-temp chilled water and desiccant dehumidification systems. 6. Learn of available retrofit and upgrade solutions that can supplement existing HVAC systems to help deliver the performance necessary to satisfy new demands.

3 Complaints? Why can t I properly control humidity in my OR? 1. Lack of understanding of basic psychometrics. 2. The HVAC systems are being designed without consideration of real world space condition requirements. 3. Inappropriate HVAC systems are being designed and installed for the task.

4 Why do we Dehumidify ORs? I m cold & clammy I m hot & sticky I m mad as hell Surgeon and staff comfort

5 Why do we Dehumidify ORs? Drier makes us feel cooler Wetter makes us feel warmer An environment with excessive humidity will make it feel warmer than it really is

6 Why do we Dehumidify ORs? 1. The combination of temperature & relative humidity is the primary component of perceived human comfort. 2. Increased levels of humidity restrict the body's evaporative processes. 3. The result of increasing humidity on human comfort is an perceived increase in air temperature. 4. This results in a decrease in human thermal comfort.

7 Why else do we Dehumidify ORs? Therapeutic reasons Instrument fogging Orthopedic adhesives Microbial growth Droplets of condensate

8 Definitions High Cool & Dehumidify Heat & Dehumidify Low Low High

9 Definitions Dry bulb temperature F (dbt): Is the temperature of air measured by a thermometer. Relative humidity % (rh): the amount of water vapor in the air, expressed as a percentage of the maximum amount that the air could hold at the given temperature 50% 100% Dew point temperature F (dpt): Is the temperature at which the air is saturated with water (100%rh). Once air is cooled to its dew point temperature, any further cooling of the air will condense moisture from it.

10 Basics This may help moving forward 1. When air-conditioning to keep a space cool we must supply conditioned air to the space that is colder than the space. 2. When air-conditioning to keep a space dry we must supply conditioned air to the space that is dryer than the space.

11 Basics o People are accustomed to describing the space temperature in terms of dry bulb temp (dbt) and relative humidity (%rh) o Dew point temperature is an indication of the amount of moisture (water) in the air. o Knowing the dew point temperature requirement of the space allows the HVAC designer to calculate how much moisture must be removed to provide proper dehumidification. o The space dew point temperature will establish the SAT required to maintain the desired humidity in the space. o Knowing the space dew point temperature allows simple troubleshooting of space humidity issues.

12 Basics 100% rh % rh dpt dbt

13 Basics Plotting any TWO known air conditions on the Psych Chart allow all the remaining conditions to be identified

14 Operating Room Design If I cool the air below 50 Fdbt (50 Fdpt) moisture will condense from the air 50 F Space (dpt) Dew Point Temperature *(required)* 100% rh 50% Space Relative Humidity (rh) 70 F Space (dbt)temperature 50 Fdbt

15 Basics This may help moving forward 1. This means (cooling based) I need to maintain my SAT below 50 F dbt (50 Fdpt) and I need chilled water cold enough to get the air (coil) to this temperature, if I want to dehumidify the air and the space?

16 Basics o If air above (warmer than) this is supplied to the space, no dehumidification will occur. o Any surface in the space below (colder than) this will condense moisture from the air..what?

17 Basics Can surface cools the air surrounding it from 70 Fdbt (50 F dpt) to 45 Fdbt and moisture in the air next to the can will begin to condense 45 F dbt 70 Fdbt / 50% rh 50 F Dew Point Temperature (dpt) Coke Bottle Effect Sweating (condensation) will form on a surface which has reached the dew-point temperature of the air which surrounds it.

18 Operating Room Design The purpose of the HVAC system in an operating room (OR) are to minimize infections, maintain patient comfort, and help facilitate patient health and recovery and maintain staff comfort. Requirement for 20-air change per hour (ach) which includes 4-ach outdoor air (20% outdoor air). Maintain positive pressure in space.

19 Operating Room Design Table 3: Ventilation Requirements for Hospitals and Outpatient Facilities Area Designation Operating Surgical Air movement relationship to adjacent area Minimum air changes outdoor air per hour Minimum total air changes per hour All air exhausted to outdoors Recirculated by means of room units Relative humidity (%) Design temperature (degrees F) Out No Texas Hospital Licensing Rules Effective June 21, 2007 Note 8: Where temperature ranges are indicated, the system shall be capable of maintaining the rooms at any point in this range. Nothing in these rules shall be construed as precluding the use of temperatures lower than those noted when the patients comfort and medical conditions make lower temperatures desirable. Note 17: Some surgeons may require room temperatures that are outside of the indicated range. All operating room design conditions shall be developed in consultation with surgeons, anesthesiologists, infection control and nursing staff.

20 Operating Room Design Orthopedic and cardiac operating room surgeons frequently request very low temperatures, often as low as 60 50%rh.

21 Operating Room Design

22 Operating Room Design Outdoor Air Load Sensible + Latent SPACE = % rh (50 Fdpt)

23 Operating Room Design Item Load Sensible Latent Lights 1-kW 3,412 Btu/hr 0 Equipment 1-kW 3,412 Btu/hr 0 6-People 3000 Btu/h 1,500 Btu/hr 1,500 Btu/hr Ventilation 440 cfm (20%) 24,330 Btu/hr 18,839 Btu/hr TOTAL 32,654 Btu/hr 20,339 Btu/hr 52,993 Btu/hr = 4.42 tons (no safety) Air reheated to 61 Fdbt (35,640 Btu/hr) Reheat is (always) required ACH drives the size of the HVAC system, not the internal loads.

24 Operating Room Design Does Reheat Matter? Thermal (Nat Gas) Energy Use Outside Air Htg 7% Reheat 65% Space Htg 15% DHW Htg 3% Dietary/Sterilizers 5% Distribution Losses 5% In order to maintain low humidity's in the space the SA Must be overcooled in order to deeply dehumidify it

25 Operating Room Design O/A: 97.2 Fdbt/68.6 Fdpt MAT = 71.1 Fdbt/54.8 Fdpt S/A: 46.0 Fdbt/46.0 Fdpt Reheat: 61.0 Fdbt SPACE : 64.5 Fdbt/50.3 Fdpt 50.3 Fdpt = 4.3 F 46.0 Fdpt

26 Operating Room Design MATRIX Texas Hospital Licensing Rules Example # OR temp F OR rh% OR dpt F dpt F SAT dpt F

27 System Types Supply Air dpt F Texas Hospital Licensing Rules ASHRAE Example

28 System Types Direct Expansion Cooling (DX) I. Packaged Roof Top Units II. Packaged Self Contained Units III. Packaged Split Systems Refrigerant based, R-410a Typical SAT 55 Fdpt Lowest SAT around 48 Fdpt

29 System Types Direct Expansion Cooling (DX) Pros Relatively inexpensive Easily understood Fairly easy to service & maintain No pumps or cooling towers required Cons Limited equipment life yrs. Inefficient at low SATs On/off capacity staging & control (unless VSC) Part load control is very difficult Requires reheat Not capable of deep dehumidification

30 DX Supply Air dpt F System Types 55 F dpt 72/60 72/50 48 F dpt 60/60 60/50

31 System Types Traditional Chilled Water System (CWS) I. Indoor Water-Cooled II. Outdoor Packaged Air-Cooled Refrigerant/water based Large tonnages available Typical LWT 44 F (coldest 40 F) Typical SAT around 53 Fdpt Lowest SAT around 45 Fdpt Lowest DPT around 43 F

32 System Types Traditional Chilled Water System (CWS) Pros Most large hospitals have CW systems Easily understood Fairly easy to service & maintain year lifespan lower SATs than DX Cons Requires pumps & piping May require a cooling tower/water and chemical consumption More maintenance required Inefficient at lower LWT Requires reheat Not capable of deep dehumidification

33 CW Supply Air dpt F System Types 72/60 72/50 53F dpt 45 F dpt 60/60 60/50

34 System Types Low-Temperature Glycol Chiller (LTCW) I. Indoor Water-Cooled II. Indoor Air-Cooled III. Outdoor Packaged Air-Cooled Refrigerant/water based Use glycol as anti-freeze Lowest SAT around 38 Fdpt

35 System Types Low-Temperature Glycol Chiller (LTCW) Pros Same as traditional chillers Capable of lower dew point temperatures Cons Higher first cost expense May be in addition to traditional DX or CW system Require glycol (antifreeze) Inefficient at lower LWTs Condensate freezing (frost) Additional duct/pipe insulation for low LATs Requires reheat

36 LTCW Supply Air dpt F System Types 60/60 60/50 72/60 72/50 38 F dpt

37 System Types Desiccant Dehumidification (DDHS) I. Indoor II. Outdoor Adsorbent: different from traditional cooling/dehumidfication system Required regeneration source Very low space dew point control

38 System Types Desiccant Dehumdification (DDHS) Different from cooling based dehumidification Attracts moisture based on vapor pressure differential

39 System Types 3. Then the wheel rotates into the reactivation airstream, the desiccant is heated by the hot reactivation air, and the desiccant releases its moisture to the reactivation air. 4. The wheel then rotates back into the process air, so it can collect more moisture from the process airstream. From Outdoors WARM To Space 1. The wheel rotates slowly between the process and reactivation airstreams. To Outdoors From Indoors or Outdoors 2. The process air flows through the wheel and the desiccant adsorbs the moisture from the air.

40 System Types Desiccant Dehumidification (DHW) Pros Commercial & industrial grades (durable) Very stable dew point space control Extremely low dew point temps Can be very energy efficient Can reduce or eliminate reheat Cons Not easily understood Requires skilled maintenance Controls may be more complex May require traditional pre-cooling system

41 Desiccant Supply Air dpt F System Types 72/60 72/50 60/60 60/50 20 F dpt OR LESS

42 Operating Room Design MATRIX OR temp F OR rh% OR dpt F dpt F SAT dpt F DX CW LTCW Des

43 System Types Process & Capacity Requirements Stage-1 cooling or Desiccant pre-cooling (MBH) Stage-2 cooling or Desiccant post-cooling (MBH) Low-Temp Chiller YES YES Desiccant Dehumidification Reactivation (MBH) NO YES Reheat (MBH) YES NO Standard-chiller nominal-tons YES YES Low-temp chiller nominal tons YES NO Standard chiller cost to operate $ 1,809 $ 4,789 Low-temp chiller cost to operate $ 6,701 $0 Reactivation cost to operate $0 $ 5,092 Reheat cost to operate $ 8,631 $ 0 Total cost to operate $ 17,141 $ 9,881 (-42%) For each 50-tons of low-temp chiller capacity replaced by desiccant dehumidification a hospital may save $5000/year or more in utility cost. Assumptions: Standard chiller COP=3.0, low temp chiller COP=2.4, operation 6-am to 6-pm M-F, 3120 hr/yr, cost of electricity = $0.07/kWh, cost of gas (reheat or regeneration) = $10/MMbtuh, boiler efficiency= 80%. YES YES

44 Retrofit Solutions

45 Retrofit Solutions DX Rooftop Unit Source of Operating Room Cooling Loads Light/Equip 10% Staff/Patient 4% Reheat 43% Minimum OA 43% Limited O/A capability = 15-20% (or less) Limited latent (dehumidification) capacity Typically no reheat capabilities Typically on-of capacity control (no cooling modulation) Typically doesn t work!

46 Retrofit Solutions Existing (10,000 cfm) DX Rooftop Unit Decoupled Desiccant (2000 cfm) Pre-Treat 100% SA 10,000 cfm 100% MA 70 F dbt 40 F dpt 2000 cfm 100% OSA 97 F dbt 34F dpt 20% OA 2000 cfm 100% OSA 83 F dbt 75 F dpt 10,000 cfm 100% SA 57 F dbt 40 F dpt Zero Reheat 60 F 55%rh 44 Fdpt 8000 cfm 100% RA 62 F dbt 45 F dpt 80% RA Handle the OA and space latent loads

47 Quick Help

48 Quick Help

49 Please visit our HTS booth at TAHFM Questions? David N. Schurk Director of Healthcare Accounts Cell: Heat Transfer Solutions Houston, TX