Geothermal Heat Pump – Passive Heating/Cooling

Boreal ® System Operation – (DC series) heating

The Boreal passive cooling heat pump incorporates one of the most advanced maintenance free system designs available today. Its simplicity is based on a heating only refrigeration system with direct groundwater cooling coils and domestic hot water generator as built in added features. Most of the parameters which may possibly lead to failure of a refrigeration system have been designed out of the units over the years and those which remain have their functions carefully controlled by internal safety mechanisms.

We can begin the explanation of the actual operation of a heat pump at any point in the system. However, for our purposes, we shall begin at the evaporator. Boreal Geothermal Inc. uses a counter flow coaxial heat exchanger which is highly resistant to freeze damage. High turbulence created by the water flow makes them relatively self-cleaning, keeping the heat pump in peak operating condition.

The layout and design of the water-to-refrigerant heat exchanger is such that our units can maintain a suction pressure equal to most conventional models on less than half the water requirement; or, if equal water is available to each unit, the Boreal unit will continue to operate safely on lower temperature water than most competitors. This feature allows the Boreal unit to operate in a much more northerly climate without danger of freeze-up.

The evaporator is maintained in a 3/4 flooded condition at all times during operation; and, since the suction line is at the top of the evaporator, there is no danger of picking up liquid in this line. Normal suction pressures are in the range of 50 to 60 psig with corresponding evaporator temperatures approximately 30 to 32° F.

Once the Freon leaves the evaporator, it is routed to a large suction line accumulator whose purpose is to ensure that absolutely no liquid Freon, which is the #1 killer of compressors, reaches our compressor. Suction gas temperatures at a point 6”
from the compressor are usually in the area of 37 to 39°F giving us a superheat of from 5 to 7° F.

Should the water supply be interrupted for some reason, the Boreal unit incorporates a low suction temperature (or pressure) cut-out switch which will automatically shut off the unit before any freeze-up can occur inside the water heat exchanger. Although the low temperature cut-out thermostat is of the automatic reset variety, a lock-out relay prevents the compressor from restarting until either the main power is interrupted or the room thermostat is turned down and then back up again.

The Freon gas travels from the suction accumulator to the compressor which makes the gas more dense and hot by the concentration of a large amount of thermal energy into a small space. The compressor used in a Boreal unit is a heavy duty Copeland Scroll compressor with one of the highest energy efficiency ratios (EER) on the market today. Long life and dependable service can be expected from this compressor since it performs a job much easier on it than what it was designed for. Typical head pressures run in the range of 200 to 250 psig which gives a compression ratio of approximately 3.5 to one.

The manufacturer has designed this compressor to work under the much more adverse conditions of an air source heat pump which could often see a compression ratio of 8 to 1, therefore current draw and wear on the compressor when used in a Boreal unit is significantly less and results in long service life. Discharge temperatures experienced by the Boreal unit are usually between 190 and 200° F. These discharge temperatures are well below accepted standards and there is no danger of internal scoring or breakdown of the oil in the system.

From the compressor the hot 198° F. discharge gas enters our tube-by-tube domestic hot water coil which is simply a superheater coil that drops the temperature of the dry discharge Freon vapor to approximately 150° F. This domestic hot water generator actually improves the performance of the entire system by initiating slight condensation of the Freon. Operation of the condenser becomes more efficient since all it’s surface is wet before it reaches it’s actual condensation temperature.

The condenser coil used in the Boreal units, has been specially designed to act as a transfer surface for both heating and cooling the household air. The coil has sufficient extra capacity to allow for dirty air filters poor air flow etc, which can produce poor performance until the situation is corrected. The return liquid line is equipped with a large filter-drier to absorb any moisture droplets that may become present in a system.

Factory procedures in silver soldering and evacuating our unit will ensure that our systems are clean and dry; however the field technician may not observe all accepted practices when he services the unit, thus admitting contaminants which the filter will catch. Boreal Geothermal Inc. uses the most efficient expansion system – a TXV to vaporize the return liquid freon. Air distribution is handled by a belt driven or direct drive ECM blower.

Direct Groundwater Cooling – “DC” Series

While the Boreal ® proves to be an outstanding performer at heating your home, it becomes even more efficient in the cooling mode. Most conventional heat pumps provide air-conditioning by reversing the refrigeration cycle, which requires the operation of the main compressor, pump and blower. Power consumption in the cooling mode is the same or higher as in the heating mode. With the Boreal unit however underground water is pumped directly to the air heat exchanger coil.

There is no need to operate the compressor which consumes approx. 80% of the power required in the heating mode since underground water below 50°F. is already sufficiently cold enough to provide direct air conditioning.

Central air conditioning and dehumidification is provided for less than 1/5 the cost of a compressor driven system. The capacity of the air-conditioning section in a Boreal unit can be adjusted by varying the flow of water to the cooling coil while that of a reversible unit is fixed to the capacaity of the heating section.

This unique feature is important since a reversible heat pump large enough to supply all the heat in a Canadian home will generally be greatly oversized in the cooling mode resulting in short cycling and insufficient dehumidification of the air.

Since proper ehumidification of the air is essential in the air conditioning mode, an oversized unit will fail to remove the moisture required leaving the occupants cold and clammy, while the Boreal unit can be tailored to remove the exact amount of humidity for comfortable living.