PROJEX Cellular Infrastructure

NOTE* This FAQ is for DC air conditioner, Split DC18
(Runs on DC power from photovoltaic panels/batteries).

What is the SplitCool DC18 unit?
The SplitCool DC18 unit is an all-DC ductless air conditioning system that is designed to run off a battery bank. The battery bank is then supplied power from an array of photovoltaic modules or other DC power source.

SplitCool is ideal for off grid applications like remote sites where grid power is unavailable or unreliable, or requires generators (with potentially complex or costly refueling logistics). This unit can also be used in applications like construction office trailers, portable classrooms, remote medical facilities or other portable or remote structures. The native 48VDC system is also directly compatible with the 48VDC power systems used in many data center, telecom or tower site applications.

What is the warranty on the unit?
The unit currently holds a 1-year warranty. It should be noted that the compressor is a hermetically sealed unit employing a brushless, permanent-magnet motor for a long and maintenance-free life cycle.

How many PV panels are needed to power the unit?
The amount of PV needed to power the unit will vary depending on the duty cycle of the system and the location and orientation of the panels. A normal duty cycle for an office might be 9 hours per day with the unit running 40% of each hour, totaling 3.6 hours of run time per day. In some cases, more run-time per hour will be needed, in other cases, more hours of service may be needed. A basic system would start with 4 or 5 250W panels and go up from there depending on duty cycle and other
requirements.

How many batteries will be needed?
See above answer to “How many PV panels are needed to power the unit?”

The amount of battery capacity needed will depend mainly on the hours of operation needed after the sun is no longer available, however batteries are required even if the usage is daytime-only, in order to stabilize the voltage. We recommend a basic configuration of eight 6-volt deep cycle batteries, size 160 Ah. Using four properly sized 12-volt batteries can accomplish the same thing. For extended operation into the evening or overnight, a larger battery plant will be needed (as well as more solar panels to
charge them).

Is there a larger capacity unit available?
Currently the only unit available is the 18,000 BTU system with one indoor unit (IDU) and one outdoor unit (ODU). However, more units will be available in other sizes at a later date. The next version on the roadmap will be an 18,000 BTU ODU with (2) two 9,000 BTU IDUs.

How is SplitCool different from the high-SEER “DC Inverter” air conditioners that are becoming so popular?
The “DC Inverter” type air conditioner is the most efficient type of AC powered air conditioner system available today. It is also the basis of the SplitCool design, we just took it a few steps further to optimize it for DC power.

In a normal “DC Inverter” air conditioner, AC power is the input, then an internal rectifier circuit converts the power to DC, and from there the power goes through an inverter circuit into the motor as variable frequency 3-Phase AC power. Therefore in order to run a normal “DC Inverter” air conditioner from solar, the solar DC would have to be inverted to AC, then converted back to DC, then inverted back to AC.

In the SplitCool system there is no rectifier and no inverter. The DC power is fed directly into the digital frequency controller where the DC power is pulsed into the brushless motor.




Does SplitCool provide heating as well as cooling?
Yes. The DC18 unit provides 18,000 BTU/hr of cooling, as well as 20,500 BTU/hr of heating.

How many square feet can SplitCool heat or cool?
This depends completely on the application and will follow the normal HVAC rules for system sizing. In order to know how many square feet the unit will heat or cool, you need to know how many BTUs are required to heat or cool the space where the unit will be installed.

On average, this unit can heat and cool a space of between 500 ft.² and 800 ft². However, this is not an absolute, and will completely depend on the building, location, insulation, usage, weather conditions and specific heating and cooling needs. A 500 ft² metal building in a warm climate with no insulation will require a lot more cooling capacity than an 800 ft² well insulated space in a cooler climate.

Is there any difference between SplitCool and a heat pump?
The SplitCool is a 48 volt DC heat pump. Other than using a direct DC power supply, it is very similar to the latest generation of ultra-high-SEER heat pumps.

How many batteries will be needed?
See above answer to “How many PV panels are needed to power the unit?”

The amount of battery capacity needed will depend mainly on the hours of operation needed after the sun is no longer available, however batteries are required even if the usage is daytime-only, in order to stabilize the voltage. We recommend a basic configuration of eight 6-volt deep cycle batteries, size 160 Ah. Using four properly sized 12-volt batteries can accomplish the same thing. For extended operation into the evening or overnight, a larger battery plant will be needed (as well as more solar panels to
charge them).

Can the unit operate with traditional on-grid (AC) power when solar is not available?
SplitCool is designed for off-grid applications. The unit itself runs off DC power, and photovoltaic modules / batteries supply DC power. Therefore, using solar panels to provide power is the most efficient way to operate the unit. However, it is possible to charge the bank of batteries with on-grid (AC) power with additional equipment such as a battery charger. Any steady 48 volt DC power supply can power the SplitCool system.

What makes the SplitCool better than using a regular air conditioner with an inverter?
1. A “regular” air conditioner uses AC power, which means that the DC power from solar panels would have to be inverted to AC power, robbing some of the power. Since solar panels natively produce DC power it makes sense that actually using DC power avoids the conversion loss.

2. A normal AC motor has two speeds - stop and go. The SplitCool uses a BLDC (Brushless DC) compressor motor with a digital controller and special control logic that controls the compressor RPMs. It is therefore a variable speed / variable refrigerant-flow compressor, resulting in a compressor that sizes itself dynamically based on load. On a hot humid day it is an 18,000 BTU unit. But it can also be a 4,000, 8,000, 12,000 BTU unit or any size in between, as needed. Of course it uses less electricity to run a 8,000 BTU system than an 18,000 BTU system, when 8,000 BTUs is all that’s needed at the moment. Most normal air conditioners simply turn on and off based on the thermostat – when temperature rises, the unit comes on and runs the compressor until the thermostat is happy. This ‘normal” normal on-off-on-off approach is very wasteful of electricity, considering that running the compressor at full speed is not always necessary. It is much more efficient to run a half-size unit for twice as long and avoid the on-off cycle as much as possible.

The cost of a SplitCool unit will be higher than the cost of a similarly sized normal air conditioner used with an inverter, however the SplitCool will use much less power. The SplitCool system cost savings occur when sizing the solar panel array and battery plant - the extremely high electrical efficiency of the SplitCool allows for using fewer solar panels and a lower battery requirement, for a lower total system cost.

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