09 Nov Energy Savings in Pharmaceutical HVAC Design
We all know that HVAC has the highest contribution to the overall energy spent in a building. In a standard pharmaceutical facility, it can consist of up to 60% of the consumed energy.
Optimizing the energy management in HVAC and related black utilities can provide substantial savings in terms of money and CO2 tons released to the atmosphere. In this post, we are going to discuss a few tips on energy savings in Pharmaceutical HVAC design and how to reduce energy consumption. The challenge is double because we should not compromise GMP regulations or safety requirements. In that way, ISPE published the Sustainability Handbook, covering these two topics. You can find more information here:
There are several ways in such an organization can certify sustainability for their new facilities. These are a few of the most important, in which HVAC energy optimization plays an important role:
1.1. NZEB (Nearly Zero Energy Buildings)
Since the beginning of 2021, all new buildings constructed within the European Union must be nearly zero energy buildings (NZEBS), according to article 9 of the EU Energy Performance Directive 2010/31/EU. The nearly zero or very low amount of energy required should be covered to a very significant extent by energy from renewable sources, including energy from renewable sources produced on-site or nearby. Another important premise to achieve this is that the facility shall be extremely energy efficient.
1.2. LEED (Leadership in Energy and Environmental Design)
LEED is a green building certification program used worldwide. Developed by the non-profit U.S. Green Building Council (USGBC), it includes a set of rating systems for the design, construction, operation, and maintenance of green buildings, homes, and neighbourhoods, which aims to help to building owners and operators be environmentally responsible and use resources efficiently.
The LEED rating system has seven areas of concentration: Sustainable Sites, Water Efficiency, Energy and Atmosphere, Materials and Resources, Indoor Environmental Quality, Innovation in Design Process and Regional Priority. Projects obtain credits in these areas to achieve certification.
More information here: https://www.usgbc.org/leed
1.3. BREEAM (Building Research Establishment Environmental Assessment Method)
BREEAM is the other largest method for assessing, rating and certifying the sustainability of buildings. The U.K. Building Research Establishment was the originator of this tool.
The BREEAM rating benchmarks enable a client and all other stakeholders to compare the performance of a building with other BREEAM rated buildings of the same type.
More information here: BREEAM Wiki – Designing Buildings
2. Ways to reduce energy consumption in pharmaceutical HVAC
Let’s see straight away some tips for energy savings in Pharmaceutical HVAC design:
2.1. Reduce the Outdoor airflow
Normally, we design the outdoor airflow to satisfy overpressure ventilation requirements. A rule of the thumb for concept design stages is to set the airflow requirements about 10-20% of the total air supply flow, and sometimes this premise is maintained until the final design. The reality is often that in most cases we require less than 10%. So, accurate analysis of the required airflow and later balancing of the system can reduce substantially the energy consumed for the make-up air.
2.2. Use of high-efficiency fans
Any fan should be provided with a VSD (Variable Speed Drive). This is the minimum consideration in terms of energy saving. Together with a flow transmitter, the system will control the required flow as the filter get clogged. Efficiency minimum IE4 for the motors is an excellent choice. The price of these motors is higher, but you should bear in mind that the operation cost during the fan lifecycle exceeds widely the purchase cost.
All the above is specific for plug fans. But there is another option to take into consideration. This is the use of EC fans array.
EC stands for electronically commutated. An EC fan has a brushless, permanent magnet DC motor with onboard electronics available for controlling a fan rotor. The efficiency class is the highest, IE5. The only problem is that a single fan can hardly provide the high static pressure normally required in pharmaceutical applications. Fan manufacturers solve this by providing a fan array in parallel. On the other hand, this allows the possibility to furnish redundancy in case of failure of one of the fans.
EC fan array
2.3. Avoid excessive Air Changes per Hour (ACH)
You can find the definition of ACH in the post About Air Changes. There is an industry-standard establishing a relationship between GMP classification and Air Changes. In most cases, this is achieved, but note the following:
- Energy consumption increases as per ACH does
- Optimal ACH depends on particle generation velocity
- By increasing ACH you can reduce the recovery time
In the graph below you can see the dependency of particle concentration in a cleanroom with the air change rate. We can observe that for normal particle generation rates, between 1,000 – 10,000 particles/(min x m3), ACH increasing affects only how fast we achieve the classification.
In some companies, there is the wrong assumption that by increasing the air change rate you will get a better quality of air. This is true only partially, so we should apply a scientific rationale to determine the optimal ACH.
2.4. Rationale outdoor temperature design
As discussed in our post Determining Outdoor Design Conditions, outdoor design conditions have a big impact on building energy consumption. This consumption is higher as the outdoor air percentage used in our systems is higher.
Oversized outdoor conditions prompt us to size up cooling/heating equipment, but with the warranty that we will keep indoor conditions within the established limits.
On the other hand, undersized conditions will require less installed power, but during hottest/coolest days of the year indoor conditions suffers.
Let’s see an example. Imagine a typical AHU supplying 15900 m3/h, and the same fresh airflow and identical heat gains. We are going to calculate the required cooling capacity for that unit by using 0.4% percentile, 1% percentile, and the worst case in 20 and 50 years for the same location, say Brussels:
The percentile gives an idea of the number of hours during a year that the temperature is higher than that temperature. So, 0.4% percentile means that the temperature will be higher than 29.1°C 0.4% of the total hours of the year (that is 35 hours per year).
Then, for the same unit conditions shown below:
We got the following cooling requirements, using the cooling and dehumidification datasheet we built here:
That means that we need 48% extra capacity between 1% percentile and the highest temperature in 50 years.
You should take into consideration if it is really necessary to increase the cooling production just to cover a few hours per year of unusually high temperature.
2.5. Tightness is important!
Cleanrooms are usually submitted to positive differential pressure, as discussed in the post Leakages Calculation. In order to achieve this differential pressure, a makeup airflow is necessary to provide to the system. To condition, this airflow is expensive, including humidifying or dehumidifying, so we should decrease the leakages through our system that will become energy losses:
- Provide and test good airtight ductwork construction, as described here Pharmaceutical HVAC Ductwork
- Provide good airtight cleanroom construction, according to VDI 2083
- Avoid unnecessary high differential pressure between rooms. 5-10 Pa between the same classification rooms and about 15 Pa between different classification rooms are normally accepted.
2.6. Modify temperature and humidity setpoints
Let’s see now how does affect the energy consumption, the energy requirements the modification of the setpoints.
For the same previous example, we are going to compare the cooling capacity required by raising up the setpoint temperature from 20 to 22 degC:
By maintaining the target relative humidity of 50% we can see that the dehumidification requirement is less either. Then, decreasing the setpoint 2 degC the cooling capacity required decreases about 8%.
Next, let’s take a look at the influence of relative humidity:
In this case, passing from 50% to 60% the cooling duty decreases about 30%.
2.7. Increase temperature and humidity deadbands
In a similar way, setting the widest possible dead bands on the temperature and humidity setpoints within the limits of the zone requirements will drop the building energy consumption.
Normally, the human comfort humidity range is set between 30-70%. If there are no process limitations (i.e. working with hygroscopic product or risk of condensation) there is no reason to use a range between 40-60%. Likewise, a temperature range of 18 – 24 degC is more energetically friendly than 20 – 22 degC.
2.8. Schedule unoccupied conditions
Pharmaceutical HVAC systems usually run 24 hours per day, and only stop for a few weeks per year during shutdowns. But in some cases, processes only take place for one or two shifts (8-16 hours out of 24). If this is your case, a good energy-saving measure is to modify the HVAC system setpoints during non-occupied periods by:
– Decrease the supply airflow (decrease ACH). As there are no people working and processes ongoing either, the particle generating rate is lower.
– Increase temperature setpoint in cooling mode, say 2 degC, as there is no need to satisfy comfort nor process conditions.
– Decrease temperature setpoint in heating mode.
It’s important to remark that if you apply these actions you should validate the occupied – non occupied switchover conditions.
2.9. Process challenges
We must not lose sight of the HVAC reason of being: to protect the processes and/or the personnel. At this point, we clearly know that with the higher level of cleanliness we require, we will need more amount of energy. And in parallel, as bigger as our cleanroom is, we will require more energy as well, independently of its classification.
Based on these premises, in terms of energy reduction, we should ask ourselves about process constraints, like for example:
- Can we design the process in a more reduced space without compromising GMP and/or ergonomics?
- Can we use closed processes? Closed processes usually require less classification level.
- Is it feasible to use RABS / Isolator technology? If aseptic processing can be carried out in a RABS or Isolator, the surrounding area could be designed in a lower classification.
- Try to install large heat-generating equipment or pieces of equipment outside the cleanroom. This will reduce the need for cooling, and we will need only to provide good ventilation.
2.10. Filter selection and maintenance
Unfortunately, in terms of energy, most of the pharmaceutical facilities will require HEPA filters, which have a large pressure drop.
If you pay attention to the filter selection, you could save an important amount of fan energy to compensate for the filter pressure drop.
Look below these proposals from the manufacturer Camfil for the same H14 filter, same dimensions (but different depth) and flow rate:
The thickest filter, model MX (90 mm depth) has a pressure drop when clean of 65 Pa, while the model MD (66 mm depth) has a pressure drop of 90 Pa (38% more).
Just take into account that HEPA filter pressure drop could arrive at 500 Pa when dirty!
2.11. Water distribution systems
Currently, almost all the designs of water distribution are based on variable pressure systems, which means using two ways valves in the terminal units. The secondary pumps for chilled water or low pressure hot water circuits modulate the required loop pressure by means of VSDs to satisfy all terminal units demand.
This design has a better energy performance than traditional constant pressure systems that use three-way valves, as they cause unnecessary fluid circulation when there is no cooling or heating demand in the terminal units.
2.12. Avoid Low Delta T in water distribution systems
Low Delta T syndrome refers to a problem in the water distribution system performance. It occurs when the temperature difference between the fluid entering and leaving a unit is lower than the coil design delta T. That cause an over pumping, necessary to satisfy the coil energy demand, with the subsequent energy increase.
Causes of the Low Delta T syndrome may vary, but the most common are:
- Incorrect design of terminal units (fan coils, reheaters, cooling and heating coils…)
- Coil lack of maintenance (fouling)
- Incorrect balancing of the water distribution system
In terms of design, we can avoid the third and most common source of the problem, reducing the possibility of a bad balancing with the following actions:
- Installation combined balancing and control valve. This type of valve controls the energy delivered to the coil instead of simply the position of the valve, by combining inlet and leaving temperature reading and even flow measurements, providing the exact cooling or heating capacity required by the coil.
You can find more information here:
- Installation of a secondary circuit (it could be injected or mixed) with a separated pump for the coil. The pump contains a flowmeter and inlet leaving temperature sensors and it will adjust the flow so that it will maintain a constant differential temperature:
2.13. Select the more efficient cooling / heating technology for your process
We should select chillers, heat pumps, boilers, etc., based on a rationale knowledge of our system. That means we should know as much accurate as possible, our facility’s cooling and heating demand to select the most adequate and efficient technology.
By using simulation software, we can get a chart like this, which is fundamental to make a choice:
Where we can see the cooling and heating demand across the year. Based on this we can select the most adequate systems.
– Chiller + boiler. Chilled water and hot water are generated independently.
– Reversible heat pump (2 pipes). This equipment provides chilled water or hot water. Simultaneous heating and cooling are not possible. The typical application is seasonal comfort cooling or heating with the scheduled changeover.
– 4 pipe heat pump. A single system provides cooling and heating on two separate loops all the year.
– Heat recovery chiller. The above system offers the possibility to recover energy when there is a simultaneous request for cooling and heating.
According to our cooling and heating needs, we can select the most efficient technology or a combination of a few of them.
The chosen system performance is highly dependent on the outdoor temperature, so it is very important to calculate the simulation considering the outdoor conditions. Hourly Analysis Program from Carrier offers that possibility, for example.
All the above collected information will help us to decide if it is better to use air-cooled or water cooled condensers.
2.14. Install Heat Recovery System
For all systems with 100% fresh air, or those where a significant amount of fresh air and extract to the outdoor, we should consider a heat recovery system.
Traditional HVAC systems use both cross-flow plate heat exchangers and rotary heat exchangers. Although these systems have a great energy recovery efficiency, they are not the most recommendable in pharmaceutical applications. Mostly in those where cross-contamination is a concern.
Rotary heat recovery exchanger
Cross flow heat recovery exchanger
The most adequate system to sort out these concerns is the run around the coil. This is a heat recovery system where the supply and exhaust airflows are completely separated. It consists of two heat exchangers hydraulically connected and circulating by means of a pump. The heat transfer fluid is usually a mix of water and glycol. In the example below we can see both coils and the hydraulic connections between them.
Reducing energy consumption in a pharmaceutical HVAC system is a challenge due to the GMP constraints, and/or biological containment of the facility. We will be forced to use high energy-consuming HVAC designs such as non-recirculating systems, a huge number of air changes per hour, or protect the process within a specific range of temperature or relative humidity.
All the above exposed tips will help us to think more deeply into our process and what are measures to apply. I hope it helps.