Frequently Asked Questions

How can HEDS provide a Return On Investment (ROI) of greater than 100%?

Although it seems strange to have an ROI greater than 100%, this may result from several different pathways.

Code compliance retrofit – If a system is in need of replacement, and it must be code compliant, and code says “no simultaneous heating and cooling”, then HEDS will most likely be the least cost option. Since the HEDS option is less expensive than the alternative, even if there were no savings, the relative ROI would be over 100%, since you are saving money, rather than spending additional money and getting a return on that added investment.

Code compliance new construction – similar to the above, if a new system must be code compliant, and code says “no simultaneous heating and cooling”, then HEDS will most likely be the least cost option. The same logic applies here.

Adding new buildings or loads – if the project consists of adding new buildings or cooling/dehumidification loads, HEDS might be less expensive than the alternatives being considered, if any expansions to the chiller plant, or piping loop is needed. For example, if you have a 1,000 ton plant, and in order to install a new facility, or integrate a new load into the plant you need to add chiller and cooling tower capacity, it may be more cost effective to do a widespread HEDS retrofit to free up an added 20% or more capacity from the same installed chiller and piping system. This would be especially true if there is a need to expand the chiller plant building or cooling tower yard and enclosure to fit the added equipment. If there is adequate chiller capacity, but you’d need to increase the CHW distribution piping to meet the new loads, HEDS may also be more cost effective, since it is possible to push 40% to 100% more BTU’s thru the same pipes, due to the higher CHW system temperature differential afforded by HEDS.

Infrastructure capacities being exceeded due to Low delta T problems - If a facility suffers from the Low Delta T Syndrome, as many do, it is possible to have not only significant energy waste, but significant stranded chiller and piping capacity that is sitting there, but that cannot be accessed due to the Low TD problem. For example, if a chiller plant is designed with a 16 degree CHW TD, and it only receives an 8 degree TD back from the system, that means that 50% of the chiller capacity cannot be utilized (8/16 = 50%). Under these, fairly typical design and TD conditions, a 1,000 ton chiller “looks” like a 500 ton chiller. It cannot load up past the 8 degree TD, so it can only deliver 50% capacity, or 500 tons. To serve a 550 ton load, you need to run two (2) 1,000 ton chillers, each at about 28% load. This is a very poor efficiency point for most chillers, especially in the summer, when cooling tower temperatures tend to be pretty high in many locations. If you do not fix the cooling coils, you will need to add CHW pipe capacity, and modify the chillers to run with an 8 Degree TD. If it is a Pri/Sec plant, you will need to double the primary loop flow, which means a complete re-pipe of the plant to single pass machines from two pass, and installing primary CHW pumps that are 6X to 8X more HP to move double the CHW flow thru them. The CHW distribution piping will also need to be replaced with pipe capable of 2X the CHW flow rate. HEDS will be less expensive in this case, so the ROI would, once again, be greater than 100%.

Is HEDS acceptable to be used in a retrofit, or only new installations?

The biggest target market is the retrofit market, where the most problems exist and the most obvious benefits are to be had. Based on our findings at two DOD test sites, in a retrofit application, HEDS has been proven to solve existing high RH/ mold/ mildew problems while, substantially cuting energy and water waste, solving the Low Delta T problem, and helping to solve cooling capacity problems. By evaluating the results that were obtained from these tests, it can be inferred that HEDS will help to solve undersized infrastructure problems, reduce manpower and maintenance costs, and lower the overall lifecycle costs associated with the cooling/dehumidification/reheat process.

If HEDS is designed into new construction, major renovation or facility expansion projects, there is the potential to actually lower overall installation costs due to reduced infrasture capacity, as well as lower overall lifecycle costs, so the Return On Investment (ROI) can actually exceed 100%.

If HEDS is designed into projects that must be ASHRAE 90.1 Energy Code compliant, there is the potential HEDS will have the least first cost impact when compared to other allowable solutions. The relative Return On Investment (ROI) can exceed 100% in these cases.

Is HEDS acceptable to be used in a retrofit, or only new installations?

Yes, based on the evaluations completed so far. The peak day cooling load reduction is approximately 20% for the two DOD test sites. When weather conditions are less severe and very low dewpoint air (<50°F) is no longer required, the cooling load reductions vary between approximately 25% and 40%. Constant air volume systems show the largest savings, ranging from 30% to 40%, as expected. VAV systems, with lower volumes of air needing reheat, shows a lower, but still significant 25% to 30% cooling load reduction. In all circumstances, the amount of reheat energy was reduced to zero for the relative humidity control process, so the reheat energy savings are 100%.

A typical subcool/reheat AHU design running a 100 ton load at the cooling coil, delivering a 54°F dewpoint at an 8°F CHW temperature differential requires 300 GPM of chilled water. How much flow is required from a HEDS unit with the same 100 ton load?

The HEDS unit will require approximately 150 GPM vs 300 GPM, and the load delivered to the chiller plant will be reduced to between 60 and 80 tons, depending upon what supply air temperature is needed to serve the end use loads.

Can HEDS handle added loads w/o additional equipment and reduce expensive upgrades?

Yes. As described above, if HEDS is incorporated for dehumidification control, it will free up additional capacity in the cooling plants and the chilled water distribution piping systems. If all loads are converted to HEDS, the chiller plant should be able serve a minimum 20% increase in loads, and the piping infrastructure should be able to serve at least 50% more capacity.

Can HEDS help to solve the “Low Delta T Syndrome”?

Yes. One of the key drivers for the Low Delta T Syndrome is undersized cooling coils and the need to serve dehumidification loads. By nature of the HEDS design, the heat transfer surface area of the cooling coils is more than 300% greater than a typical 6 row, 10 fins per inch coil at the normal 550 feet per minute face velocity. HEDS will typically be delivering 1.5-2 times the actual operating chilled water system temperature differential

Can HEDS improve efficiencies of added facilities?

Yes. When new facilities are being added, or facilities are being rehabilitated or expanded, the HEDS design can be incorporated to reduce lifecycle costs. If a chiller plant has reached the maximum capacity that it can deliver, the piping infrastructure may also be maxed out as described above. The piping system may actually be maxed out prior to the plant being maxed out. If the plant and piping system capacity is maxed out, there are two remedies – 1) add more chiller, cooling tower, pumping and piping capacity, and potentially an addition to the chiller plant building to house the new equipment, which can all add up to tens of millions of dollars just to add one more building, or 2) install HEDS projects to make better use of the installed equipment and piping by decreasing the cooling loads on the plant and increasing the chilled water system temperature differential and CHW piping infrastructure capacity.

Can HEDS produce water?

Yes, especially at deep dehumidification conditions.

Can HEDS reduce Infrastructure Costs?

Yes. A benefit of HEDS is that the chilled water flow rate required to meet peak day cooling/dehumidification needs will be reduced by approximately 50% by a combination of reduced cooling plant loads and increased chilled water system temperature differentials provided by the very large cooling coils.

On sites that may be stretching the limits of their piping infrastructure, the ability to meet the same cooling loads with a 50% reduction in the flow rate can mean that the avoided costs from not having to replace the piping infrastructure can cover the most or all of the costs of HEDS retrofit projects. While not a HEDS project, one of our team members has been working with the University of Southern California since 1992, and has helped raise their CHW system temperature differential (TD) from 8°-9°F during peak summer months in 1992, up to 25°-27°F today. This has allowed USC to avoid replacing their underground piping, as the installed piping can now move 300% more BTU’s per gallon due to the 3 times higher chilled water temperature differential. This is a savings of over $10,000,000 for the campus.

Desiccant wheels and rotary HX wheels require that the exhaust streams be filtered to reduce clogging of the wheels. Does HEDS have this requirement?

HEDS does not require any use of the exhaust air streams, so there is no worry about cross-contamination of the exhaust and supply airstreams.

Does HEDS require a 2-pipe water distribution system, or will it also work with a 4-pipe system?

HEDS works with both system types. One of the advantages of the HEDS design is that it can provide cooled and dehumidified air with a 2-pipe system, without requiring electric reheat or complex and hard to maintain desiccant wheel based equipment. With a 2-pipe system in the winter, the hot water return (HWR) temperature approaches the coil entering air temperature, since there is so much heat transfer surface area available and the air is moving at such a low velocity thru the coils. This means that with a 180°F hot water supply (HWS) temperature, you will end up with a 100°F to 120°F temperature differential, delivering substantial efficiency gains to the HW system. With a 4-pipe system, the Cooling Recovery Coil (CRC) can either be piped to operate as a heating coil in the winter (via a Belimo 6-way valve or the equivalent), or a heating coil can be utilized in the unit. If the CRC is used as a heating coil, the chemical treatment systems for the HW and CHW should be checked for compatibility

For 24/7 load types, what is the potential energy savings associated with a HEDS project?

This depends to a great extent on the dewpoint temperature that is required and the supply air temperature that is required. For MAU’s, (Make up Air Units), PTOA’s (Pre-Treat Outside Air units) and DOAS’s (Dedicated Outdoor Air Systems) that need to deliver low RH tempered air to the spaces or the downstream HVAC system, the cooling load savings can be in excess of 20%. If the required dewpoint temperature is in the mid-50’s and the required supply air temperature is in the mid 60’s, HEDS can deliver between 30% and 40% cooling load reductions.

The associated overall energy savings can be in the 45% to 65% range due to the overall systems impact of the load reductions at the central plant.

For non-24/7 load types, what is the potential energy savings associated with a HEDS project?

This is very site specific, but if the base case facility runs their HVAC system 24/7 and the occupancy only requires 5/12 operation, the savings can be in the 60% to 70% range. This is a blended combination of 40% to 50% runtime reduction and 20% to 40% cooling loads reduction savings. With HEDS, the RH-control related reheat energy gets cut by 100%. Many facilities use electric reheat, so this can be a significant cost savings.

How can HEDS reduce HVAC system run time in non-24/7 load facilities?

Many, if not most, office type facilities in humid climates that are supposed to run on a 5/12 schedule, actually run their HVAC systems 24/7 during the heat of the summer in an attempt to maintain acceptable comfort and RH conditions within the buildings. That means that they are simultaneously cooling then reheating the air for nearly 3,600 hours per year when the building is unoccupied.

If the facility is in a tropical location, similar systems must simultaneously cool then reheat the air for 8,760 hours per year. This is an incredible waste of energy, and for locations where fuel must be shipped in, there is added energy waste from the tankers for the fuel shipping process.

HEDS units are equipped with very large, high capacity cooling and cooling recovery coils. These large coils and the HEDS design and control strategies allow the loads to be brought under control far more rapidly than any of the typically designed options. It is typical to see facilities that have been retrofit with high capacity cooling coils be able to significantly reduce their run times. In the case of humid to tropical locations, experience shows that run times can be reduced by up to 90+ hours per week.

How does HEDS comply with ASHRAE 90.1 in meeting and exceeding the energy code standard?

Based on our knowledge of the code requirements, we believe that it is ASHRAE 90.1 compliant.

How does the air pressure drop through a run around coil based system compare to a HEDS system?

Total run-around coil AHU pressure drop will typically be in the 1.0” to 1.2” range. Typical HEDS coil air pressure drops are less than 0.5” WC.

How much energy can be saved in Hospital/OSHPD operating room facilities?

In many OSHPD spaces, there is the ability for a HEDS project to cut the circulated air volumes down by 75% when the spaces are not occupied. During these non-occupied hours, HEDS controls are set up to deliver low dewpoint air at very low RH conditions to prevent the spaces from becoming subcooled, which has the tendency to create areas of condensation which can lead to mold and other biological growth.

A recent evaluation for just this facility configuration is showing a greater than 80% cooling, dehumidification and reheat energy savings. This is not necessarily typical, as the base case utilizes very energy intensive direct expansion systems for dehumidification.

Typical savings for Hospital/OSPHD operating room facilities are in the 50% heating and cooling energy savings range.

How will the HEDS design work with an existing boiler during the heating season?

If the HEDS system is used in a 2-pipe system, the hot water system temperature differential will be larger than with a typical coil selection, allowing a few different things to occur – substantial pump energy savings due to the larger HW system temperature differential that occurs due to the much larger coils, potential infrastructure savings when facilities are added – the existing piping infrastructure can carry at least 25% more BTU’s per gallon of water delivered. With a 4 pipe system, either a typical heating coil can be installed, or, if the hot water and chilled water systems have compatible chemical treatment systems, the CRC or cooling coils can be used as heating coils with a switchover valve system, similar to the Belimo 6-way valves. When it is time for boiler upgrade or augmentation, condensing type boilers that can deliver efficiencies in the high 90% range can be used, since it would be possible to serve the heating loads with 100°F to 120°F hot water supply temperatures vs. needing 180°F to 200°F required by typical designs.

In many cases, condensed water is carried off of the cooling coils into the downstream ductwork and re-evaporated into the airstream. The water can saturate the insulation systems and become mold infested. Can HEDS stop this from happening?

Yes. The HEDS design typically uses cooling coil airstream face velocities that are 50% lower than typical cooling coil face velocities. HEDS also uses cooling coil heights that can be 50% shorter than typical designs, to prevent the buildup of condensed water in the cooling coil finned surface. These two attributes make it nearly impossible to carry water off of the HEDS cooling coil. If there were ever a situation that water was carried off of the cooling coil, it would hit the cooling recovery coil, and either be drained from the unit or re-evaporated into the airstream.

In the answer above, it was noted that the cooling load savings can range from 30% to 40%, but the total energy savings may range from 45% to 65% range. How can the overall energy savings can be greater than the cooling loads % reduction?

Most modern chiller plants utilize Variable Frequency Drives (VFD’s) on their pumping and cooling tower systems. VFD equipped fans and pumps respond to reduced loads at a near cubic relationship. A HEDS related 25% cooling load reduction with a corresponding CHW system temperature differential increase of 40%+ can result in a 50%+ savings for the pumps and CTF motors. If the facility is equipped with a properly selected VFD chiller, the savings can be even greater. Additionally, the reheat energy can be a significant figure, and that has been reduced by 100%.

Is a separate heating coil also needed downstream of the HEDS system in my air handler?

In a 2-pipe system, the cooling coil or CRC can be used as the heating coil, so a downstream heating coil is not required for heating.

In a four-pipe system, if the CRC or cooling coils are not used in a switchover design to act as heating coils in the winter, there will be the need for either an upstream or downstream heating coil to provide heat to the facility. We will be evaluating the data to determine if a downstream heating coil is needed when it is cool and muggy outside and the internal cooling loads are low, but still exist.

Is HEDS scalable down to room sized solutions, such as fan coil units?

Other options available for dehumidification and RH control are generally not able to be cost effectively scaled down to Fan Coil Unit (FCU) sizes. This precludes their use in a multiplicity of facility types. However, given the simplicity of the HEDS design, the system can be cost effectively scaled down to match needs at the room level.

It seems like the CHW temperature differential of most dehumidification systems is very low. That precludes the use of piping the chillers to operate in series. Can HEDS utilize series chiller operation to increase the capacity and efficiency of the upstr

The higher CHW system TD provided by HEDS can provide the conditions required for the series chiller configuration, and the associated energy savings and capacity enhancement.…

Many desiccant based systems have supply air temperatures in excess of 90°F to 100°F+ and need post-unit cooling coils and chiller capacity. Does HEDS have this requirement?

HEDS does not need added cooling coils after the CRC.

Many desiccant wheels need a 200°F to 300°F heat source to regenerate the wheel. Does HEDS require this additional heat source?

HEDS does not have any form of a rotating wheel, and there are no desiccant components in the system at all, so there is no need for a high temperature regeneration source, as no regeneration is required.

Since the return temperature for the chilled water is increasing above a standard ten-degree delta T, does this mean that the chiller also needs to be evaluated to see if it can handle this large spread of water temperatures without causing issues?

Typically not. We have been using 30°F to 36°F CHW system TD’s since the mid 1980’s in new and retrofit projects using chillers designed for 10°F to 15°F TD’s with the two basic mechanical designs out there – primary/secondary, (Pri/Sec) and primary-only variable flow, (POVF), sometimes called “Variable Primary Flow” or “VPF”.

Both designs automatically accommodate for higher than “normal” chilled water distribution system temperature splits by recirculating some of the cold supply water back into the chiller return line when site TD’s greatly exceed chiller design TD - this lowers the effective TD that the chillers see. With a Pri/Sec system, as the secondary CHW loop flow drops off due to the higher system TD, the primary loop flow remains the same, which recirculates more chilled water from the supply into the return line, creating the desired TD thru the chiller. As an example, if there was a 500-ton load that was operating at a 20-degree TD, (use 45°F/65°F as example) and the chiller was originally designed for a 10-degree TD, the secondary CHW flow would be 600 GPM. The design primary CHW flow would be 1,200 GPM – consisting of 600 GPM of recirculated 45-degree supply water, and 600 GPM of 65 degree return water for a blended temperature of 55 degrees at 1200 GPM into the chiller.

Similarly, a POVF/VPF system will reduce flow thru the chiller as the site TD increases and the site flow is reduced. At some point in time, the minimum CHW flow limit thru the chiller evaporator is reached, and the minimum CHW evaporator flow bypass valve will start to open, sending some of the cold supply water back to blend with the CHWR and the return water temperature entering the chiller will be reduced.

To dramatically improve chiller plant efficiency, chiller plants with high potential TD’s can be slightly modified to allow a “series or parallel” piping arrangement with the addition of a few valves and some control logic. These valves allow the chillers to run in parallel when the TD’s are normal, and in series when the TD’s get to about 15°F to 18°F. This allows the upstream chiller to operate at an increased efficiency of at least 25% due to lower lift required on the upstream chiller.

An example of these design strategies is a low temperature CHW TES based system we designed for a Pacific Gas and Electric facility, the SRVCC. The peak day CHW loop TD ever recorded was 45°F, consisting of 32°F CHWS temperature and 77°F CHWR temperature. The chillers were designed for a 15°F split each, using POVF and the series-parallel design, we create chilled water at 32°F at less than 0.60 kW/ton for the entire chiller plant electrical consumption, including chillers, CHW pumps, CDW pumps TES pumps and CT fans.

Typical, existing, old chillers can usually operate with CHW flow rates of less than 50% of design flow, if the flows are varied at less than 10% every couple of minutes. Cutting the flow in half results in a TD of double the design TD.

The cooling coils in HEDS units are much larger than in “normal” AHU’s. How does the fan energy become reduced instead of increased?

HEDS coils have typically 300%+ greater heat transfer surface area than typical dehumidification AHU’s. This added surface area is a combination of more rows, which add pressure drop, a higher fins per inch count, which also adds air pressure drop, as well as greater width or height, which reduces air velocity and reduces air pressure drop. The reduced air velocity component of the design overcomes the impact of the deeper coils with higher fins per inch density. Normal AHU’s can have combined coil pressure drops of 0.80” to 1.0” WC, and run around coil AHU’s can have combined coil pressure drops of 0.90” to 1.1” WC. Desiccant based systems can have added pressure drops of 2.0” for the inlet air, as well as an added 2" pressure drop for the exhaust side. The typical pressure drop for the HEDS units is less than 0.5" total across both coils.

Turbine air inlet cooling (TAIC) systems can form ice crystals in the inlet air stream, potentially causing turbine damage. Can HEDS eliminate the problem?

Yes. Yes. By raising the inlet air temperature several degrees above the dewpoint temperature, ice crystal formation can be avoided.

What is the lowest dewpoint temperature that HEDS can achieve?

A low dewpoint version of the HEDS system can provide 34°F to 35°F supply air dewpoint temperatures at appropriate chilled water supply temperature conditions from the central plant. Custom engineered HEDS units can provide supply air dewpoint temperatures as low as 20° F.