Before we go into the specifics of the different designs, we will briefly explain the working principle of a heat pump. Regardless of which type of heat pump you use, they are always efficient heating systems that extract free environmental heat by consuming a small amount of energy in the form of electricity.
The heat pump works like an inverted refrigerator, extracting thermal energy from the ambient medium and routing it to the heating system in the building. There, the energy can be used for DHW heating and/or central heating backup. In the private sector, the primary energy sources used are the ambient air, groundwater and geothermal heat.
Since the initial investment is higher for water-to-water heat pumps and brine-to-water heat pumps (also known as a geothermal heat pumps), many building owners opt for air-to-water heat pumps. They have many plus points, particularly in terms of flexible installation. This can be a deciding factor when renovating existing buildings, for example.
INTRODUCTION
Electricity Prices rose up significantly in many Canadian Provinces and US states. This rising utility rates trend will continue in the future, since federal / local governments are gradually pushing citizens to consume less and less Energy by tightening energy efficiency requirements in every new version of building code. This is a major challenge for both home owners (or to be home owners), designers, contractors and equipment suppliers since they must come up with new products in order to meet up with the higher sustainability standard.
With many Canadians spending more time at home due to long winter, COVID-19 Pandemic and aging population, demand for natural light in indoor spaces is on the rise. More natural light means larger Fenestrated Building Envelopes which require more and more energy to provide an acceptable indoor living standard.
With Rising Energy Prices, tougher Environmental Regulations combined with demographic and living standard changes, Air to Water Heat Pumps are the most affordable answer to the previously listed requirements. Air to Water Heat Pumps are HVAC devices (called Mini Air Cooled Chillers in Europe) producing Chilled/Hot Water (or Water/Glycol Mixture) that can be used for Space Heating and Cooling as well as Domestic Hot Water (DHW) Heating. ATW Heat Pumps are equipped with a DC Inverter Compressor and the Split Configuration has the EVI (Enhanced Vapor Injection) technology, which make them able to operates at a temperature range from -25°C to 45°C
AIR TO WATER (ATW) HEAT PUMPS CONFIGURATIONS
Monoblock Air to Water Heat Pump
Monoblock ATW Heat Pump is comprised of one piece destined to be installed outside. When used in outdoor climates with peak winter temperatures below 0°C (32°F), a Propylene Glycol/Water Mixture shall be used as a heat transfer fluid to avoid freezing. Mixture Glycol Concentration % depends on lowest winter temperature. In most major Canadian Cities a 50% Water / Propylene Glycol Mixture is used.
Monoblock ATW Heat Pump requires external pump for pumping heat transfer fluid (whether Water or Water/Glycol Mixture). In Winter time, Monoblock ATW Heat pump goes into cooling mode (in other terms it draws heat from the indoor space) to defrost the ice accumulated on its evaporator. Monoblock Heat Pump requires an external heat source for its defrost operation in winter. Controller of this type of Heat Pump supports modulating speed pumps and is equipped with a PWM (Pulse Width Modulation) control signal for controlling fluid circulation pump speed.
Split Air to Water Heat Pump
Split ATW Heat Pump is comprised of two pieces. One piece called the outdoor unit is destined to be installed outside and the second piece, called the indoor unit is destined to be installed inside. Split ATW Heat Pump does not require Water/Glycol Mixture in cold climates, since the link between indoor and outdoor unit is made by refrigerant copper lines (refrigerant is a fluid that does not freeze).
Split ATW Heat Pump controller is equipped with a PWM (Pulse Width Modulation) control signal for controlling fluid circulation pump speed. Variable Speed Pump helps increasing the energy efficiency of the heat pump and improve summer performance when heat pump goes into humidity control mode. In Winter time, Split ATW Heat pump goes into cooling mode (in other terms it draws heat from the indoor space) to defrost the ice accumulated on its evaporator. It also requires an external heat source for its defrost operation in winter.
ATW Configurations Cost Analysis
Air to Water Heat Pump can be used to provide either Chilled Water or Hot Water and Pre-Heated DHW or Chilled Water and Hot Water and Pre-Heated DHW. In both cases price difference is driven by machine, glycol, pump and manpower individual prices.
Heating or Cooling with DHW Pre-Heating
Simultaneous Heating and Cooling with DHW Pre-Heating
The above schematics depict the 2 most common installations of Air to Water Heat Pumps. The one on the left is for places where simultaneous Cooling / Heating is rare, so one tank with indirect coil is used to preheat DHW to temperatures as high as 130°F (or 55°C) and the other tank is used for either space heating or space cooling. In the schematic on the right, One indirect tank is used for DHW pre-heating and space heating and the other tank is dedicated for chilled water.
When Heat Pump are used to serve largely Fenestrated Properties with a South and North Exposures, area beside the southern façade could have a cooling demand (even in mid-winter temperatures) and area beside the northern façade will have a heating demand.
Item
Link to Forlssman
Monoblock HSS030V2LM
SPLIT HSS030V2LS
Heat Pump Selling Price
5,235
7,521
50% Glycol - 16 Pails - Selling Price (required to fill 2 x 40 US Gallons Tanks)
3,840
Manhours Cost for the Installation of Refrigerant Copper Lines Between Indoor and Outdoor Unit
480
Total Cost (CAD $)
9,075
8,001
CONCLUSION
Even though Monoblock Heat Pumps are cheaper than the split ones, Complete Installation of Split ATW heat pump is always cheaper to customer. Assuming that water is free to be used as a heat transfer fluid in Split Heat Pumps installations, the cost of buying a good quality glycol with proper inhibitor concentration as well as the cost of circulation pump make the Monoblock heat pump installation more expensive.
Monoblock Heat Pumps are more popular among DIY customers because people think it's cheaper (before calculating the overall cost of the project) and is easier to install (plug and play device). Split ATW Heat Pump requires a professional for the installation and commissioning of the refrigerant copper lines which makes it not appealing to some DIY Customers.
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