Engineers Newsletter: Impact of DOAS Supply-Air Dew Point Temperature

Home , Dew

providing insights for today’s hvac system designer Engineers Newsletter volume 49–1 Impact of DOAS Supply-Air Dew Point Temperature on Space Humidity

Using a dedicated outdoor-air system Introduction (DOAS) to condition outdoor air Isn’t 55°F Dew Point Good separately from recirculated air can Enough? make it easier to verify that sufficient In buildings that use zone-level terminal ventilation airflow reaches each zone. units for cooling and heating (such as VRF, For many HVAC design engineers, a And when that outdoor air is water-source heat pumps, fan-coils, small common design practice has been to dehumidified, so that it is drier than DX split systems, PTACs, chilled beams, or the space, it can also help prevent high specify the dedicated OA unit to space humidity levels. sensible-cooling terminal units), a separate dehumidify the outdoor air to a 55°F dedicated outdoor-air system is often used dew point temperature (which equates But many of the dedicated outdoor-air to provide ventilation. systems designed and installed today to 64.6 gr/lb at sea level) and then reheat it to a “neutral” dry-bulb temperature are not dehumidifying adequately. This As the name implies, this system uses a Engineers Newsletter examines one (70°F for example). reason why this may be the case. dedicated unit to condition all the outdoor air (OA) being brought in for ventilation (Figure 1). Meanwhile, a terminal unit provides cooling or heating in each zone.

Figure 1. Dedicated outdoor-air system (DOAS).

dedicated outdoor-air unit

terminal unit terminal unit

terminal unit

However, depending on the desired Figure 2. Dehumidifying to 55°F dew point may actually add latent load to the space. conditions in the space, this conditioned 90% outdoor air (labeled “CA” in the figures 85 80% 85 throughout) may actually be wetter than 180 the space. For example, if the desired 70% 160 space conditions are 73°F dry bulb and OA 93°F DBT 80 80 50 percent relative humidity (RH), this 80°F WBT 60% OA 140 70°F DBT equates to a humidity ratio of 60.6 gr/lb. CA 75 50% 55°F DPT wet bulb temperature (°F) 75 64.6 gr/lb Therefore, the humidity ratio of the 120 70 40% conditioned outdoor air (CA) is higher space 73°F DBT 70 50% RH 100 than the desired space humidity ratio, 60.6 gr/lb 65 50% RH 30% 65 meaning that the DOAS is adding latent dehumidify 60 load to the space. This requires the 80 60 CA 55 64.6 gr/lb t zone-level terminal unit to have 20% 55 dew point temperature (°F) a reheat 60 r sufficient dehumidification (latent) 50 space 60.6 gr/lb 50 capacity to remove this added latent 45 45 40 40 humidity ratio (grains of moisture per pound dry air) 40 load, and the latent load generated in 45 • Conditioned outdoor10% air (CA) the space (due to people, infiltration, 30 is wetter than space 30 20 etc.). Otherwise, the space humidity 73°F DBT • DOAS adds latent load to space 20 0 level will rise higher than desired. 0 30 40 50 60 70 80 90 100 110 To demonstrate this impact, consider dry bulb temperature (°F) the example K-12 classroom detailed in Table 1.

The dedicated OA unit delivers 350 cfm Table 1. Example of K-12 classroom. of outdoor air (CA) directly to this design load part load classroom at 55°F dew point and 70°F 2 dry bulb (Figure 3). The terminal unit floor area (Az) 750 ft then conditions only recirculated air (RA) design population (Pz) 26 people to cool or heat the space to the desired space dry-bulb temperature (DBTspace) 73°F dry-bulb temperature. space relative humidity desired (RHspace) 50% space sensible cooling load (Q )1 20,300 Btu/hr 12,200 Btu/hr Because the conditioned outdoor air is space, sensible 2 slightly cooler than the space, it offsets space latent load (Qspace, latent) 4030 Btu/hr 4030 Btu/hr 1140 Btu/hr of the space sensible space sensible heat ratio (SHR)3 0.83 0.75 4 cooling load: 1.085 × 350 cfm × (73°F – zone outdoor airflow (Voz) 350 cfm 350 cfm 70°F). At design cooling load conditions (Table 1), this leaves the remaining 1 Determined using load calculation software 2 ® 19,160 Btu/hr (20,300 – 1140) of 26 people × 155 Btu/hr/person (per 2017 ASHRAE Handbook, page 18.4, assuming “seated, very light work” for the occupant activity level) 3 sensible load to be offset by the Space SHR = Qspace,sensible / (Qspace,sensible + Qspace,latent) 4 2 2 ® terminal unit. Vbz = 350 cfm = (26 people x 10 cfm/person) + (750 ft x 0.12 cfm/ft ), per ASHRAE Standard 62.1-2016, ® Table 6.2.2.1. Voz = Vbz / Ez = 350 cfm / 1.0 (per ASHRAE Standard 62.1-2016, Table 6.2.2.2, assuming Assuming this terminal unit is sized to conditioned OA delivered directly to the space at a temperature cooler than the space) cool recirculated air to 55°F dry bulb at design conditions, the terminal unit serving this classroom is sized for 980 cfm: 19,160 Btu/hr = 1.085 × Vsa × (73°F Figure 3. DOAS and terminal unit serving this example classroom. – 55°F).

from DOAS

zone-level terminal unit

980 cfm 55°F DBT 350 cfm 70°F DBT, 55°F DPT 73°F DBT

2 Trane Engineers Newsletter volume 49-1 providing insights for today’s HVAC system designer Depicted on a psychrometric chart Figure 4. DOAS supplying 55°F dew point at design (full-load) conditions. (Figure 4), the dedicated OA unit 90% dehumidifies the warm, humid outdoor 85 80% 85 air (OA) to a 55°F dew point and then OA 93°F DBT 180 80°F WBT reheats it to 70°F dry bulb (CA). The 70% CA 70°F DBT 160 terminal unit cools 980 cfm of 80 80 (DOAS: 350 cfm, 2.65 tons) 55°F DPT recirculated air (RA) from 73°F to 55°F 60% RA 73°F DBT OA 140 dry bulb (SA). The classroom receives (space) 55% RH 50% wet bulb temperature75 (°F) 75 a total of 1330 cfm (350 cfm of (0.83 space SHR) 55°F DBT 120 conditioned outdoor air from the DOAS SA 40% (terminal: 980 cfm, 1.93 tons) 54°F DPT 70 70 plus 980 cfm of cooled supply air from 59°F DBT 100 the terminal unit), depicted as the SA+CA 65 (1330 cfm) 54°F DPT 30% 65 combined condition labeled “SA+CA” 60 80 60 in Figure 4. CA 55

RA (space) 20% 55 dew point temperature (°F) 60 Following the 0.83 space SHR line 50 SA SA+CA 50 from point SA+CA, the resulting 45 45 40 40 humidity ratio (grains of moisture per pound dry air) 40 condition in the space (RA) is 73°F dry 45 10% bulb and 55 percent RH; higher than 30 30 20 the 50 percent RH desired. 20 0 0 Why is this? The dedicated OA unit 30 40 50 60 70 80 90 100 110 dehumidifies the incoming outdoor air dry bulb temperature (°F) to a 55°F dew point, which is at a higher humidity ratio than the desired space humidity ratio. Therefore, the space, the terminal unit needs to cool to 59°F dry bulb (SA), so the classroom DOAS still adds some latent load to the this 740 cfm of recirculated air to 59°F receives a total of 1090 cfm (SA+CA). space, and the terminal unit does not dry bulb: 11,060 Btu/hr = 1.085 × 740 cfm Following the part-load 0.75 space SHR have sufficient dehumidification × (73°F – DBTsa). line, the resulting condition in the space is (latent) capacity to remove this added 73°F dry bulb and 61 percent RH; much latent load plus the space latent load. At this part-load condition, the outdoor air higher than the 50 percent RH desired. (OA) is cooler, but still humid (Figure 5). The dedicated OA unit still dehumidifies For this example classroom, arbitrarily What happens at part-load it to the same 55°F dew point before specifying the dedicated OA unit to conditions? For this example reheating it to 70°F dry bulb (CA). dehumidify the outdoor air to a 55°F dew classroom, assume that the space point did not result in the desired space sensible cooling load is only 60 As described, the terminal unit now cools humidity level, especially at part load. percent of the design load, or 12,200 740 cfm of recirculated air (RA) from 73°F Btu/hr (Table 1). However, all the students are still present in the classroom, so the space latent load Figure 5. DOAS supplying 55°F dew point at part-load conditions. remains unchanged (4030 Btu/hr). This causes a reduction in the space SHR, 90% 85 80% 85 from 0.83 at design to 0.75 at this part- OA 69°F DBT 180 load condition. 66°F WBT 70% CA 70°F DBT 160 80 80 (DOAS: 350 cfm) 55°F DPT The DOAS continues to deliver 350 60% cfm of conditioned outdoor air to the RA 73°F DBT 140 (space) 61% RH 50% wet bulb temperature75 (°F) 75 classroom at the same conditions, so (0.75 space SHR) it still offsets 1140 Btu/hr of the space 59°F DBT 120 SA 40% sensible cooling load. That leaves the (terminal: 740 cfm) 58°F DPT 70 70 remaining 11,060 Btu/hr 63°F DBT 100 SA+CA 65 OA (12,200 – 1140) of sensible load to be (1090 cfm) 57°F DPT 30% 65 60 offset by the terminal unit. 80 60 SA RA (space) 55

20% 55 dew point temperature (°F) Because the sensible load in the space SA+CA CA 60 50 is lower, the terminal unit controller 50 45 45 40 40 humidity ratio (grains of moisture per pound dry air) has reduced its fan speed in this 40 example, delivering its minimum 45 10% 30 30 airflow of 740 cfm (980 cfm × 0.75, 20 20 assuming 75 percent minimum fan 0 0 speed). To offset the remaining 30 40 50 60 70 80 90 100 110 11,060 Btu/h of sensible load in the dry bulb temperature (°F)

providing insights for today’s HVAC system designer Trane Engineers Newsletter volume 49-1 3

What if instead of 55°F dew point, Figure 6. DOAS supplying 45°F dew point at design (full-load) conditions. the dedicated OA unit is selected 90% 85 80% 85 for a lower dew point? As depicted OA 93°F DBT 180 in Figure 6, at design (full-load) 80°F WBT 70% conditions, the dedicated OA unit now CA 70°F DBT 160 80 80 (DOAS: 350 cfm, 3.38 tons) 45°F DPT dehumidifies the warm, humid 60% outdoor air (OA) to 45°F dew point, RA 73°F DBT OA 140 (space) 50% RH 50% wet bulb temperature75 (°F) 75 but still reheats it to 70°F dry bulb (0.83 space SHR)

(CA). Again, the terminal unit cools 55°F DBT 120 SA 40% 980 cfm of recirculated air (RA) from (terminal: 980 cfm, 1.64 tons) 53°F DPT 70 70 73°F to 55°F dry bulb (SA). 100 SA+CA 59°F DBT 65 (1330 cfm) 51°F DPT 30% 65

Because the conditioned outdoor air 60 80 60 (CA) is drier, the combined 1330 cfm 55

20% 55 dew point temperature (°F) of air supplied to the space (SA+CA) SA RA (space) 60 50 50 is drier, and the resulting condition in SA+CA 45 45 40 40 humidity ratio (grains of moisture per pound dry air) the space is 73°F dry bulb at the CA 40 desired 50 percent RH. 45 10% 30 30 20 At the same example part-load 20 0 condition (Figure 7), the outdoor air 0 30 40 50 60 70 80 90 100 110 (OA) is still dehumidified to 45°F dew dry bulb temperature (°F) point and reheated to 70°F dry bulb (CA). The terminal unit, now operating at minimum fan speed, cools 740 cfm Figure 7. DOAS supplying 45°F dew point at part-load conditions. of recirculated air (RA) from 73°F to 90% 85 59°F dry bulb (SA). The resulting 80% 85 OA 69°F DBT 180 condition in the space is 73°F dry bulb 66°F WBT 70% and 51 percent RH. CA 70°F DBT 160 80 80 (DOAS: 350 cfm) 45°F DPT 60% As mentioned, arbitrarily specifying RA 73°F DBT 140 (space) 51% RH 50% the dedicated OA unit to deliver 55°F wet bulb temperature75 (°F) 75 (0.75 space SHR) dew point may not result in the space 59°F DBT 120 SA 40% humidity level desired, especially at (terminal: 740 cfm) 54°F DPT 70 70 part load. A lower dew point (45°F in SA+CA 63°F DBT 100 65 OA this example) may be needed to (1090 cfm) 51°F DPT 30% 65 achieve the desired results. 60 80 60

SA 20% 55 dew point temperature (°F) RA (space) 60 50 50 SA+CA 45 45 40 CA 40 humidity ratio (grains of moisture per pound dry air) Determining the Required 40 45 10% 30 30 DOAS Supply-Air Dew 20 Point 20 0 0 The “right” DOAS supply-air dew 30 40 50 60 70 80 90 100 110 dry bulb temperature (°F) point for a given application depends on the type of space and the indoor humidity level desired, as well as the type of terminal units used (see sensible-only terminal units sidebar). Sensible-only terminal units

Some types of terminal units (such as chilled beams, radiant cooling panels, or sensible-cooling terminals) are designed to provide only sensible cooling, no dehumidification. When this type of terminal equipment is used, the DOAS is the only source of dehumidification and must be sized to dehumidify the OA dry enough so that it maintains the space dew point low enough to avoid condensation on the sensible-only terminals. For example, if 57°F water is supplied to the terminals, the DOAS might be designed to prevent the space dew point from rising above 55°F, creating a 2°F buffer.

4 Trane Engineers Newsletter volume 49-1 providing insights for today’s HVAC system designer The following latent load equation can be used to determine the required Space Latent Load (Qspace,latent) humidity ratio (Wca) of the conditioned outdoor air supplied by the DOAS: The pie chart in Figure 8 depicts the sources of latent load for an example K-12 classroom. In this case, the ventilation (outdoor) air accounts for almost two-thirds of the total latent load. The remaining one-third are the space latent loads, which occur within the boundaries of the Qspace,latent = 0.69 × Voz × (Wspace – conditioned space (mostly due to people and infiltration). Wca) The latent load due to the outdoor air affects the dehumidification capacity of the equipment, where: but only the space portion of the latent load (Qspace,latent) dictates how dry the supply air • Qspace,latent = latent load in the space, Btu/hr must be.These loads will vary for different space types, based on activity level and occupant density. • Voz = outdoor airflow delivered to the space, cfm Figure 8. Latent loads for example K-12 classroom. • Wspace = desired humidity ratio in the space, gr/lb

• Wca = required humidity ratio of the conditioned outdoor air supplied by the DOAS, gr/lb infiltration people The value 0.69 in this equation is not a constant, but is derived from the properties of air at ventilation space latent loads (outdoor air) permeance (Q ) “standard” conditions. Air at other conditions space, latent and elevations will cause this factor to change.

For the example K-12 classroom described earlier, the space latent load

is estimated to be 4030 Btu/hr and the Source: Humidity Control Design Guide, ASHRAE© 2001, p. 278 required outdoor airflow is 350 cfm (see Table 1). If the desired space conditions are 73°F dry bulb and 50 This is dry enough to offset the entire For the example K-12 classroom (top bar in percent RH, this equates to a space latent load and keep the space the chart), if the desired space conditions humidity ratio of 60.6 gr/lb in the humidity ratio (Wspace) at the desired are 73°F dry bulb and 50 percent RH, the space. Using the previous equation, in level. conditioned outdoor air needs to be order to remove the entire space dehumidified to approximately a 45°F dew latent load, this 350 cfm of outdoor air The required DOAS supply-air dew point (as calculated previously). But if a must be dehumidified to 43.9 gr/lb, point varies for other space types and higher dew point is supplied by the DOAS, which equates to approximately 45°F other space conditions. Figure 9 space humidity will be higher. dew point. compares this required dew point for several different space types, For spaces with lower ventilation rates, 4030 Btu/hr = 0.69 × 350 cfm × (60.6 assuming minimum ventilation rates such as an auditorium or conference room, gr/lb – Wca), so Wca = 43.9 gr/lb and default occupant densities per a very low dew point may be required; or ASHRAE Standard 62.1. the DOAS might be designed to deliver more-than-minimum ventilation airflow to sufficiently dehumidify these spaces.

Figure 9. Comparison of DOAS supply-air dew points for various space types and conditions.

73°F DBT 75°F DBT K-12 classroom 50% RH 60% RH 73°F DBT 75°F DBT Lecture hall (fixed seats) 50% RH 60% RH 73°F DBT 75°F DBT Auditorium 50% RH 60% RH 73°F DBT 75°F DBT Conference room 50% RH 60% RH 73°F DBT 75°F DBT Office space 50% RH 60% RH 73°F DBT 75°F DBT Lobby 50% RH 60% RH 73°F DBT Hotel guest bedroom 75°F DBT 50% RH 60% RH 73°F DBT 75°F DBT Barracks 50% RH 60% RH 73°F DBT Retail sales floor 75°F DBT 50% RH 60% RH 20 25 30 35 40 45 50 55 Required dew point temperature of conditioned OA to maintain desired space humidity level, °F (This assumes default occupant density, 155 or 200 Btu/h/person space latent load, and sea level elevation.)

providing insights for today’s HVAC system designer Trane Engineers Newsletter volume 49-1 5

Figure 10. Sensible cooling energy wasted when dehumidified outdoor air is reheated to “neutral”. Neutral versus cold air 90% 85 80% 85 Some HVAC engineers design the 180 dedicated outdoor-air system to 70% CA 80 160 reheat the dehumidified outdoor air OA CC 80 to a “neutral” dry-bulb temperature 60% OA 140 sensible cooling energy spent 50% (70°F for example). But this wastes wet bulb temperature755 (°F) 75 dehumidification energy when the zones also require cooling reheat 120 40% cooling. coil coil 70 70 100 65 When a chilled-water or refrigerant 30% 65 60 coil is used to dehumidify the outdoor 80 60 air (OA to CC in Figure 10), a 55 20% 55 dew point temperature (°F) chilled-water or refrigerantspace coil 60 byproduct of that dehumidification 50 50 process is sensible cooling. The dry- 45 45 40 40 humidity ratio (grains of moisture per pound dry air) CC CA Wca 40 bulb temperature of the air leaving 45 reheat coil 10% 30 30 the cooling coil (CC) is colder than the 20 sensible cooling wasted 20 space. If this dehumidified air is then DBTca 0 reheated to neutral (CC to CA), some 0 30 40 50 60 70 80 90 100 110 of the sensible cooling performed by dry bulb temperature (°F) the dedicated OA unit is wasted.

If the zones need cooling, why not make use of the sensible cooling already done by the dedicated OA However, there may be times when just enough (CC to CA) to avoid unit? Otherwise the terminal units reheating is needed to avoid over-cooling delivering colder-than-desired air to the will be forced to offset more of the a space. Or, depending on what dew spaces (to 55°F in this example). This space sensible cooling load, point is required, some engineers might takes advantage of the sensible cooling increasing their energy use. not be comfortable with delivering the air effect of this cold, dehumidified air, that cold. In Figure 11, the outdoor air is thereby reducing the need for re-cooling To address the inefficiency of neutral- dehumidified to 45°F dew point, which at the zone-level terminal units. temperature air, the 2016 version of corresponds to a dry-bulb temperature of ASHRAE Standard 90.1 added a new about 45°F (CC). Rather than reheating requirement that prohibits a DOAS this air to neutral, consider reheating it from reheating the dehumidified outdoor air to any warmer than 60°F Figure 11. DOAS supplying 45°F dew point and 55°F dry bulb at design (full-load) conditions. dry bulb, whenever the majority of zones require cooling. This applies even if recovered heat is used. 90% 85 80% 85 OA 93°F DBT 180 80°F WBT 70% CA 55°F DBT 160 80 80 (DOAS: 350 cfm, 3.38 tons) 45°F DPT 6.5.2.6 Ventilation Air Heating Control 60% Units that provide ventilation air to multiple RA 73°F DBT OA 140 (space) 49% RH 50% wet bulb temperature75 (°F) 75 zones and operate in conjunction with zone (0.83 space SHR) heating and cooling systems shall not use heating or heat recovery to warm supply air SA 55°F DBT 120 70 40% above 60°F when representative building (terminal: 690 cfm, 1.19 tons) 52°F DPT 70 loads or outdoor air temperature indicate that 100 SA+CA 55°F DBT 65 the majority of zones require cooling. (1040 cfm) 50°F DPT 30% 65

60 ASHRAE 90.1-2016 80 60

20% 55 dew point temperature (°F) SA RA (space) 60 50 50 SA+CA 45 45 40 40 humidity ratio (grains of moisture per pound dry air) CC CA 40 45 10% 30 30 20 20 0 0 30 40 50 60 70 80 90 100 110 dry bulb temperature (°F)

6 Trane Engineers Newsletter volume 49-1 providing insights for today’s HVAC system designer However, when the space is drier, the Final Thoughts enthalpy of the recirculated air entering Resources the terminal unit is lower, reducing its In most climates, the dedicated OA required cooling capacity. When the [1] ANSI/ASHRAE, Standard 62.1-2016, Ventilation unit should be sized to dehumidify DOAS delivers 55°F dew point air, the for Acceptable Indoor Air Quality. Atlanta: ASHRAE. 2016. the outdoor air to a dew point that is terminal unit requires 1.93 tons to cool low enough to offset the space latent 980 cfm of recirculated air to 55°F dry [2] ANSI/ASHRAE/IES, Standard 90.1-2016, Energy load and maintain space humidity bulb (Figure 4). But when the DOAS Standard for Buildings Except Low-Rise level at or below the desired limit. delivers 45°F dew point air, the Residential Buildings. Atlanta: ASHRAE. 2016. Arbitrarily specifying a unit to deliver terminal unit requires only 1.64 tons of [3] ASHRAE, Inc. Design Guide for Dedicated 55°F dew point may not result in the capacity (Figure 6). Outdoor Air Systems. Atlanta: ASHRAE, 2017. space humidity level desired, especially at part load. A lower dew Finally, if the DOAS is designed to [4] ASHRAE, Inc. ASHRAE Handbook – point is often needed to achieve the dehumidify the OA to 45°F dew point, Fundamentals. Atlanta: ASHRAE, 2017. but then reheat it to only 55°F dry bulb, desired results. [5] Murphy, J. 2018. “Common Pitfalls in the this cool air often allows the terminal Design and Operation of DOAS.” ASHRAE The “right” dew point for a given unit to be downsized even further. In Journal (September): 10-17. application depends on the type of this example, the design airflow of the space and the indoor humidity level terminal unit is reduced to 690 cfm and [6] Trane®. CoolSense® Integrated Outdoor Air desired, as well as the type of its cooling capacity is reduced to 1.19 system catalog. SYS-APG004*-EN. 2019. terminal units used. tons (Figure 11). [7] Trane. Dedicated Outdoor Air Systems application guide. SYS-APG001*-EN. 2019. Note that a dedicated OA unit sized to The impact on the cost of the overall dehumidify to a lower dew point will system depend on the relative [8] Trane. Variable Refrigerant Flow Systems require more capacity than one sized installation costs of the DOAS versus system catalog. SYS-APG007*-EN. 2020. to dehumidify to a higher dew point the terminal system. [9] Trane. “Horizon® Dedicated Outdoor Air (Table 2). For the example classroom Systems.” https://www.trane.com/Horizon. By John Murphy, Trane. To subscribe or view described in this EN, dehumidifying previous issues of the Engineers Newsletter visit 350 cfm from design outdoor air trane.com/EN. Send comments to conditions to 55°F dew point requires [email protected]. 2.65 tons of capacity (Figure 4), whereas dehumidifying this air to 45°F dew point requires 3.38 tons (Figure 6).

Table 2. Impact of DOAS supply-air conditions (example K-12 classroom).

DOAS supply-air conditions

70°F DBT 70°F DBT 55°F DBT 55°F DPT 45°F DPT 45°F DPT (Figure 4) (Figure 6) (Figure 11)

dedicated OA unit capacity 2.65 tons 3.38 tons 3.38 tons

terminal unit capacity 1.93 tons 1.64 tons 1.19 tons

terminal unit design airflow 980 cfm 980 cfm 690 cfm

providing insights for today’s HVAC system designer Trane Engineers Newsletter volume 49-1 7

Join your local Trane office for the 2020 Engineers Newsletter LIVE! Mark your calendar!

Impact of DOAS Dew Point on Space Humidity. Dedicated outdoor-air systems (DOAS) are used in a variety of building types to provide ventilation; and when the outdoor air is dehumidified, a DOAS can help prevent high space humidity levels. But many of the systems designed and installed today are not dehumidifying adequately. This ENL will demonstrate how space humidity levels are affected by the DOAS discharge-air conditions, at both full load and part load.

Indoor Agriculture: HVAC System Design Considerations. Conditioning spaces for plants instead of humans introduces new challenges. This ENL will discuss plants, the dehumidification challenges they pose, and how precision cooling for indoor agriculture is different compared to comfort cooling. We’ll also discuss common air- and waterside system configurations used to maintain space conditions to ensure a healthy crop.

Applying VRF for a Complete Building Solution. This ENL builds upon the 2014 VRF program “Applying Variable Refrigerant Flow” with detailed discussions on several considerations. Topics will include: when to use heat recovery instead of heat pump configurations, how to scale VRF systems to include other building systems, ventilation delivery, humidity management and more.

Decarbonize HVAC Systems. Many municipalities are taking action to reduce their carbon emissions which includes the reduction, or removal, of natural gas for heating. The HVAC industry will face the challenge of heating buildings with electric heat. This ENL will cover the motivation to electrify, areas currently effected by this trend, and potential systems to meet electrification needs.

Contact your local Trane office for dates and details.

Horizon™ Dedicated Outdoor Air Systems Trane® Horizon™ Dedicated Outdoor Air Systems are designed specifically to condition up to 100% of outdoor air year-round, reduce latent loads, enhance the entire building system’s comfort and energy efficiency, and maintain your building’s health.

Visit www.trane.com/Horizon

This newsletter is for informational purposes only and does not constitute legal advice. Trane believes the facts and suggestions presented here to be accurate. However, final design and application decisions are your responsibility. Trane disclaims any responsibility for actions taken on the material presented.

Trane, the Circle Logo, CoolSense, and Horizon are registered trademarks of Trane in the United States For more information, contact your local Trane and other countries. ASHRAE is trademark of the American Society of Heating, Refrigerating, and Air- office or e-mail us at [email protected] Conditioning Engineers, Inc. ANSI is a registered trademark of American National Standards Institute. All trademarks referenced are the trademarks of their respective owners.

8 Trane Engineers Newsletter volume 49-1 ADM-APN073-EN (March 2020)